Block Device Guide

Red Hat Ceph Storage 4

Managing, creating, configuring, and using Red Hat Ceph Storage Block Devices

Red Hat Ceph Storage Documentation Team

Abstract

This document describes how to manage, create, configure, and use Red Hat Ceph Storage Block Devices.
Red Hat is committed to replacing problematic language in our code, documentation, and web properties. We are beginning with these four terms: master, slave, blacklist, and whitelist. Because of the enormity of this endeavor, these changes will be implemented gradually over several upcoming releases. For more details, see our CTO Chris Wright's message.

Chapter 1. Introduction to Ceph block devices

A block is a set length of bytes in a sequence, for example, a 512-byte block of data. Combining many blocks together into a single file can be used as a storage device that you can read from and write to. Block-based storage interfaces are the most common way to store data with rotating media such as:

  • Hard drives
  • CD/DVD discs
  • Floppy disks
  • Traditional 9-track tapes

The ubiquity of block device interfaces makes a virtual block device an ideal candidate for interacting with a mass data storage system like Red Hat Ceph Storage.

Ceph block devices are thin-provisioned, resizable and store data striped over multiple Object Storage Devices (OSD) in a Ceph storage cluster. Ceph block devices are also known as Reliable Autonomic Distributed Object Store (RADOS) Block Devices (RBDs). Ceph block devices leverage RADOS capabilities such as:

  • Snapshots
  • Replication
  • Data consistency

Ceph block devices interact with OSDs by using the librbd library.

Ceph block devices deliver high performance with infinite scalability to Kernel Virtual Machines (KVMs), such as Quick Emulator (QEMU), and cloud-based computing systems, like OpenStack, that rely on the libvirt and QEMU utilities to integrate with Ceph block devices. You can use the same storage cluster to operate the Ceph Object Gateway and Ceph block devices simultaneously.

Important

To use Ceph block devices, requires you to have access to a running Ceph storage cluster. For details on installing a Red Hat Ceph Storage cluster, see the Red Hat Ceph Storage Installation Guide.

Chapter 2. Ceph block device commands

As a storage administrator, being familiar with Ceph’s block device commands can help you effectively manage the Red Hat Ceph Storage cluster. You can create and manage block devices pools and images, along with enabling and disabling the various features of Ceph block devices.

2.1. Prerequisites

  • A running Red Hat Ceph Storage cluster.

2.2. Displaying the command help

Display command, and sub-command online help from the command-line interface.

Note

The -h option still displays help for all available commands.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the client node.

Procedure

  1. Use the rbd help command to display help for a particular rbd command and its subcommand:

    Syntax

    rbd help COMMAND SUBCOMMAND

  2. To display help for the snap list command:

    [root@rbd-client ~]# rbd help snap list

2.3. Creating a block device pool

Before using the block device client, ensure a pool for rbd exists, is enabled and initialized.

Note

You MUST create a pool first before you can specify it as a source.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the client node.

Procedure

  1. To create an rbd pool, execute the following:

    Syntax

    ceph osd pool create POOL_NAME PG_NUM
    ceph osd pool application enable POOL_NAME rbd
    rbd pool init -p POOL_NAME

    Example

    [root@rbd-client ~]# ceph osd pool create example 128
    [root@rbd-client ~]# ceph osd pool application enable example rbd
    [root@rbd-client ~]# rbd pool init -p example

Additional Resources

  • See the Pools chapter in the Red Hat Ceph Storage Storage Strategies Guide for additional details.

2.4. Creating a block device image

Before adding a block device to a node, create an image for it in the Ceph storage cluster.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the client node.

Procedure

  1. To create a block device image, execute the following command:

    Syntax

    rbd create IMAGE_NAME --size MEGABYTES --pool POOL_NAME

    Example

    [root@rbd-client ~]# rbd create data --size 1024 --pool stack

    This example creates a 1 GB image named data that stores information in a pool named stack.

    Note

    Ensure the pool exists before creating an image.

Additional Resources

2.5. Listing the block device images

List the block device images.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the client node.

Procedure

  1. To list block devices in the rbd pool, execute the following (rbd is the default pool name):

    [root@rbd-client ~]# rbd ls
  2. To list block devices in a particular pool, execute the following, but replace POOL_NAME with the name of the pool:

    Syntax

    rbd ls POOL_NAME

    Example

    [root@rbd-client ~]# rbd ls swimmingpool

2.6. Retrieving the block device image information

Retrieve information on the block device image.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the client node.

Procedure

  1. To retrieve information from a particular image, execute the following, but replace IMAGE_NAME with the name for the image:

    Syntax

    rbd --image IMAGE_NAME info

    Example

    [root@rbd-client ~]# rbd --image foo info

  2. To retrieve information from an image within a pool, execute the following, but replace IMAGE_NAME with the name of the image and replace POOL_NAME with the name of the pool:

    Syntax

    rbd --image IMAGE_NAME -p POOL_NAME info

    Example

    [root@rbd-client ~]# rbd --image bar -p swimmingpool info

2.7. Resizing a block device image

Ceph block device images are thin provisioned. They do not actually use any physical storage until you begin saving data to them. However, they do have a maximum capacity that you set with the --size option.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the client node.

Procedure

  1. To increase or decrease the maximum size of a Ceph block device image:

    Syntax

    [root@rbd-client ~]# rbd resize --image IMAGE_NAME --size SIZE

2.8. Removing a block device image

Remove a block device image.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the client node.

Procedure

  1. To remove a block device, execute the following, but replace IMAGE_NAME with the name of the image you want to remove:

    Syntax

    rbd rm IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd rm foo

  2. To remove a block device from a pool, execute the following, but replace IMAGE_NAME with the name of the image to remove and replace POOL_NAME with the name of the pool:

    Syntax

    rbd rm IMAGE_NAME -p POOL_NAME

    Example

    [root@rbd-client ~]# rbd rm bar -p swimmingpool

2.9. Moving a block device image to the trash

RADOS Block Device (RBD) images can be moved to the trash using the rbd trash command. This command provides more options than the rbd rm command.

Once an image is moved to the trash, it can be removed from the trash at a later time. This helps to avoid accidental deletion.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the client node.

Procedure

  1. To move an image to the trash execute the following:

    Syntax

    rbd trash mv [POOL_NAME/] IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd trash mv test_img01

    Once an image is in the trash, a unique image ID is assigned.

    Note

    You need this image ID to specify the image later if you need to use any of the trash options.

  2. Execute the rbd trash list for a list of IDs of the images in the trash. This command also returns the image’s pre-deletion name. In addition, there is an optional --image-id argument that can be used with rbd info and rbd snap commands. Use --image-id with the rbd info command to see the properties of an image in the trash, and with rbd snap to remove an image’s snapshots from the trash.
  3. To remove an image from the trash execute the following:

    Syntax

    rbd trash rm [POOL_NAME/] IMAGE_ID

    Example

    [root@rbd-client ~]# rbd trash rm d35ed01706a0

    Important

    Once an image is removed from the trash, it cannot be restored.

  4. Execute the rbd trash restore command to restore the image:

    Syntax

    rbd trash restore [POOL_NAME/] IMAGE_ID

    Example

    [root@rbd-client ~]# rbd trash restore d35ed01706a0

2.10. Enabling and disabling image features

You can enable or disable image features, such as fast-diff, exclusive-lock, object-map, or journaling, on already existing images.

Note

The deep flatten feature can be only disabled on already existing images but not enabled. To use deep flatten, enable it when creating images.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the client node.

Procedure

  1. To enable a feature.

    Syntax

    rbd feature enable POOL_NAME/IMAGE_NAME FEATURE_NAME

    1. To enable the exclusive-lock feature on the image1 image in the data pool:

      Example

      [root@rbd-client ~]# rbd feature enable data/image1 exclusive-lock

      Important

      If you enable the fast-diff and object-map features, then rebuild the object map:

      + .Syntax

      rbd object-map rebuild POOL_NAME/IMAGE_NAME
  2. To disable a feature.

    Syntax

    rbd feature disable POOL_NAME/IMAGE_NAME FEATURE_NAME

    1. To disable the fast-diff feature on the image2 image in the data pool:

      Example

      [root@rbd-client ~]# rbd feature disable data/image2 fast-diff

2.11. Working with image metadata

Ceph supports adding custom image metadata as key-value pairs. The pairs do not have any strict format.

Also, by using metadata, you can set the RADOS Block Device (RBD) configuration parameters for particular images.

Use the rbd image-meta commands to work with metadata.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the client node.

Procedure

  1. To set a new metadata key-value pair:

    Syntax

    rbd image-meta set POOL_NAME/IMAGE_NAME KEY VALUE

    Example

    [root@rbd-client ~]# rbd image-meta set data/dataset last_update 2016-06-06

    This example sets the last_update key to the 2016-06-06 value on the dataset image in the data pool.

  2. To remove a metadata key-value pair:

    Syntax

    rbd image-meta remove POOL_NAME/IMAGE_NAME KEY

    Example

    [root@rbd-client ~]# rbd image-meta remove data/dataset last_update

    This example removes the last_update key-value pair from the dataset image in the data pool.

  3. To view a value of a key:

    Syntax

    rbd image-meta get POOL_NAME/IMAGE_NAME KEY

    Example

    [root@rbd-client ~]# rbd image-meta get data/dataset last_update

    This example views the value of the last_update key.

  4. To show all metadata on an image:

    Syntax

    rbd image-meta list POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd data/dataset image-meta list

    This example lists the metadata set for the dataset image in the data pool.

  5. To override the RBD image configuration settings set in the Ceph configuration file for a particular image:

    Syntax

    rbd config image set POOL_NAME/IMAGE_NAME  PARAMETER VALUE

    Example

    [root@rbd-client ~]# rbd config image set data/dataset rbd_cache false

    This example disables the RBD cache for the dataset image in the data pool.

Additional Resources

  • See the Block device general options section in the Red Hat Ceph Storage Block Device Guide for a list of possible configuration options.

2.12. Moving images between pools

You can move RADOS Block Device (RBD) images between different pools within the same cluster.

During this process, the source image is copied to the target image with all snapshot history and optionally with link to the source image’s parent to help preserve sparseness. The source image is read only, the target image is writable. The target image is linked to the source image while the migration is in progress.

You can safely run this process in the background while the new target image is in use. However, stop all clients using the target image before the preparation step to ensure that clients using the image are updated to point to the new target image.

Important

The krbd kernel module does not support live migration at this time.

Prerequisites

  • Stop all clients that use the source image.
  • Root-level access to the client node.

Procedure

  1. Prepare for migration by creating the new target image that cross-links the source and target images:

    Syntax

    rbd migration prepare SOURCE_IMAGE TARGET_IMAGE

    Replace:

    • SOURCE_IMAGE with the name of the image to be moved. Use the POOL/IMAGE_NAME format.
    • TARGET_IMAGE with the name of the new image. Use the POOL/IMAGE_NAME format.

    Example

    [root@rbd-client ~]# rbd migration prepare data/source stack/target

  2. Verify the state of the new target image, which is supposed to be prepared:

    Syntax

    rbd status TARGET_IMAGE

    Example

    [root@rbd-client ~]# rbd status stack/target
    Watchers: none
    Migration:
                source: data/source (5e2cba2f62e)
                destination: stack/target (5e2ed95ed806)
                state: prepared

  3. Optionally, restart the clients using the new target image name.
  4. Copy the source image to target image:

    Syntax

    rbd migration execute TARGET_IMAGE

    Example

    [root@rbd-client ~]# rbd migration execute stack/target

  5. Ensure that the migration is completed:

    Example

    [root@rbd-client ~]# rbd status stack/target
    Watchers:
        watcher=1.2.3.4:0/3695551461 client.123 cookie=123
    Migration:
                source: data/source (5e2cba2f62e)
                destination: stack/target (5e2ed95ed806)
                state: executed

  6. Commit the migration by removing the cross-link between the source and target images, and this also removes the source image:

    Syntax

    rbd migration commit TARGET_IMAGE

    Example

    [root@rbd-client ~]# rbd migration commit stack/target

    If the source image is a parent of one or more clones, use the --force option after ensuring that the clone images are not in use:

    Example

    [root@rbd-client ~]# rbd migration commit stack/target --force

  7. If you did not restart the clients after the preparation step, restart them using the new target image name.

2.13. The rbdmap service

The systemd unit file, rbdmap.service, is included with the ceph-common package. The rbdmap.service unit executes the rbdmap shell script.

This script automates the mapping and unmapping of RADOS Block Devices (RBD) for one or more RBD images. The script can be ran manually at any time, but the typical use case is to automatically mount RBD images at boot time, and unmount at shutdown. The script takes a single argument, which can be either map, for mounting or unmap, for unmounting RBD images. The script parses a configuration file, the default is /etc/ceph/rbdmap, but can be overridden using an environment variable called RBDMAPFILE. Each line of the configuration file corresponds to an RBD image.

The format of the configuration file format is as follows:

IMAGE_SPEC RBD_OPTS

Where IMAGE_SPEC specifies the POOL_NAME / IMAGE_NAME, or just the IMAGE_NAME, in which case the POOL_NAME defaults to rbd. The RBD_OPTS is an optional list of options to be passed to the underlying rbd map command. These parameters and their values should be specified as a comma-separated string:

OPT1=VAL1,OPT2=VAL2,…​,OPT_N=VAL_N

This will cause the script to issue an rbd map command like the following:

rbd map POOLNAME/IMAGE_NAME --OPT1 VAL1 --OPT2 VAL2

Note

For options and values which contain commas or equality signs, a simple apostrophe can be used to prevent replacing them.

When successful, the rbd map operation maps the image to a /dev/rbdX device, at which point a udev rule is triggered to create a friendly device name symlink, for example, /dev/rbd/POOL_NAME/IMAGE_NAME, pointing to the real mapped device. For mounting or unmounting to succeed, the friendly device name must have a corresponding entry in /etc/fstab file. When writing /etc/fstab entries for RBD images, it is a good idea to specify the noauto or nofail mount option. This prevents the init system from trying to mount the device too early, before the device exists.

Additional Resources

  • See the rbd manpage for a full list of possible options.

2.14. Configuring the rbdmap service

To automatically map and mount, or unmap and unmount, RADOS Block Devices (RBD) at boot time, or at shutdown respectively.

Prerequisites

  • Root-level access to the node doing the mounting.
  • Installation of the ceph-common package.

Procedure

  1. Open for editing the /etc/ceph/rbdmap configuration file.
  2. Add the RBD image or images to the configuration file:

    Example

    foo/bar1    id=admin,keyring=/etc/ceph/ceph.client.admin.keyring
    foo/bar2    id=admin,keyring=/etc/ceph/ceph.client.admin.keyring,options='lock_on_read,queue_depth=1024'

  3. Save changes to the configuration file.
  4. Enable the RBD mapping service:

    Example

    [root@client ~]# systemctl enable rbdmap.service

Additional Resources

  • See the The rbdmap service section of the Red Hat Ceph Storage Block Device Guide for more details on the RBD system service.

2.15. Monitoring performance of Ceph Block Devices using the command-line interface

Starting with Red Hat Ceph Storage 4.1, a performance metrics gathering framework is integrated within the Ceph OSD and Manager components. This framework provides a built-in method to generate and process performance metrics upon which other Ceph Block Device performance monitoring solutions are built.

A new Ceph Manager module,rbd_support, aggregates the performance metrics when enabled. The rbd command has two new actions: iotop and iostat.

Note

The initial use of these actions can take around 30 seconds to populate the data fields.

Prerequisites

  • User-level access to a Ceph Monitor node.

Procedure

  1. Enable the rbd_support Ceph Manager module:

    Exmaple

    [user@mon ~]$ ceph mgr module enable rbd_support

  2. To display an "iotop"-style of images:

    Example

    [user@mon ~]$ rbd perf image iotop

    Note

    The write ops, read-ops, write-bytes, read-bytes, write-latency, and read-latency columns can be sorted dynamically by using the right and left arrow keys.

  3. To display an "iostat"-style of images:

    Example

    [user@mon ~]$ rbd perf image iostat

    Note

    The output from this command can be in JSON or XML format, and then can be sorted using other command-line tools.

2.16. Additional Resources

Chapter 3. The rbd kernel module

As a storage administrator, you can access Ceph block devices through the rbd kernel module. You can map and unmap a block device, and displaying those mappings. Also, you can get a list of images through the rbd kernel module.

Important

Kernel clients on Linux distributions other than Red Hat Enterprise Linux (RHEL) are permitted but not supported. If issues are found in the storage cluster when using these kernel clients, Red Hat will address them, but if the root cause is found to be on the kernel client side, the issue will have to be addressed by the software vendor.

3.1. Prerequisites

  • A running Red Hat Ceph Storage cluster.

3.2. Create a Ceph Block Device and use it from a Linux kernel module client

As a storage administrator, you can create a Ceph Block Device for a Linux kernel module client in the Red Hat Ceph Storage Dashboard. As a system administrator, you can map that block device on a Linux client, and partition, format, and mount it, using the command line. After this, you can read and write files to it.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • A Red Hat Enterprise Linux client.

3.2.1. Create a Ceph Block Device for a Linux kernel module client using Dashboard

You can create a Ceph Block Device specifically for a Linux kernel module client using the Dashboard web interface by enabling only the features it requires.

Prerequisites

  • A running Red Hat Ceph Storage cluster.

Procedure

  1. Log in to the Dashboard.
  2. On the navigation bar, click Pools:

    Click pools
  3. Click the Create button:

    Click create
  4. In the dialog window, set the name:

    Set name
  5. Set the Pool type to replicated:

    replicated
  6. Set the Placement Group (PG) number:

    Set PG number

    For assistance in choosing the PG number, use the PG calculator. Contact Red Hat Technical Support if unsure.

  7. Set the replicated size:

    Replicated size
  8. Enable the rbd application:

    Enable rbd
  9. Click Create pool:

    Click Create pool
  10. View the notifications indicating the pool was created successfully:

    Creation notifications
  11. Click Block:

    Click Block
  12. Click Images:

    Click Images
  13. Click Create:

    Click Create
  14. Configure the following: 1 the desired image name, 2 set Pool to the pool created earlier, 3 set the desired size of the image, 4 ensure Layering and Exclusive lock are the only enabled features:

    Set image parameters
  15. Click CreateRBD:

    Clck CreateRBD
  16. View the notification indicating the image was created successfully:

    Image creation notification

Additional Resources

3.2.2. Map and mount a Ceph Block Device on Linux using the command line

You can map a Ceph Block Device from a Red Hat Enterprise Linux client using the Linux rbd kernel module. After mapping it, you can partition, format, and mount it, so you can write files to it.

Prerequisites

Procedure

  1. On the Red Hat Enterprise Linux client node, enable the Red Hat Ceph Storage 4 Tools repository:

    Red Hat Enterprise Linux 7

    [root@client1 ~]# subscription-manager repos --enable=rhel-7-server-rhceph-4-tools-rpms

    Red Hat Enterprise Linux 8

    [root@client1 ~]# subscription-manager repos --enable=rhceph-4-tools-for-rhel-8-x86_64-rpms

  2. Install the ceph-common RPM package:

    Red Hat Enterprise Linux 7

    [root@client1 ~]# yum install ceph-common

    Red Hat Enterprise Linux 8

    [root@client1 ~]# dnf install ceph-common

  3. Copy the Ceph configuration file from a Monitor node to the Client node:

    scp root@MONITOR_NODE:/etc/ceph/ceph.conf /etc/ceph/ceph.conf

    Example

    [root@client1 ~]# scp root@cluster1-node2:/etc/ceph/ceph.conf /etc/ceph/ceph.conf
    root@192.168.0.32's password:
    ceph.conf                                                                          100%  497   724.9KB/s   00:00
    [root@client1 ~]#

  4. Copy the key file from a Monitor node to the Client node:

    scp root@MONITOR_NODE:/etc/ceph/ceph.client.admin.keyring /etc/ceph/ceph.client.admin.keyring

    Example

    [root@client1 ~]# scp root@cluster1-node2:/etc/ceph/ceph.client.admin.keyring /etc/ceph/ceph.client.admin.keyring
    root@192.168.0.32's password:
    ceph.client.admin.keyring                                                          100%  151   265.0KB/s   00:00
    [root@client1 ~]#

  5. Map the image:

    rbd map --pool POOL_NAME IMAGE_NAME --id admin

    Example

    [root@client1 ~]# rbd map --pool block-device-pool image1 --id admin
    /dev/rbd0
    [root@client1 ~]#

  6. Create a partition table on the block device:

    parted /dev/MAPPED_BLOCK_DEVICE mklabel msdos

    Example

    [root@client1 ~]# parted /dev/rbd0 mklabel msdos
    Information: You may need to update /etc/fstab.

  7. Create a partition for an XFS file system:

    parted /dev/MAPPED_BLOCK_DEVICE mkpart primary xfs 0% 100%

    Example

    [root@client1 ~]# parted /dev/rbd0 mkpart primary xfs 0% 100%
    Information: You may need to update /etc/fstab.

  8. Format the partition:

    mkfs.xfs /dev/MAPPED_BLOCK_DEVICE_WITH_PARTITION_NUMBER

    Example

    [root@client1 ~]# mkfs.xfs /dev/rbd0p1
    meta-data=/dev/rbd0p1            isize=512    agcount=16, agsize=163824 blks
             =                       sectsz=512   attr=2, projid32bit=1
             =                       crc=1        finobt=1, sparse=1, rmapbt=0
             =                       reflink=1
    data     =                       bsize=4096   blocks=2621184, imaxpct=25
             =                       sunit=16     swidth=16 blks
    naming   =version 2              bsize=4096   ascii-ci=0, ftype=1
    log      =internal log           bsize=4096   blocks=2560, version=2
             =                       sectsz=512   sunit=16 blks, lazy-count=1
    realtime =none                   extsz=4096   blocks=0, rtextents=0

  9. Create a directory to mount the new file system on:

    mkdir PATH_TO_DIRECTORY

    Example

    [root@client1 ~]# mkdir /mnt/ceph

  10. Mount the file system:

    mount /dev/MAPPED_BLOCK_DEVICE_WITH_PARTITION_NUMBER PATH_TO_DIRECTORY

    Example

    [root@client1 ~]# mount /dev/rbd0p1 /mnt/ceph/

  11. Verify that the file system is mounted and showing the correct size:

    df -h PATH_TO_DIRECTORY

    Example

    [root@client1 ~]# df -h /mnt/ceph/
    Filesystem      Size  Used Avail Use% Mounted on
    /dev/rbd0p1      10G  105M  9.9G   2% /mnt/ceph

Additional Resources

3.3. Getting a list of images

Get a list of Ceph block device images.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. To mount a block device image, first return a list of the images:

    [root@rbd-client ~]# rbd list

3.4. Mapping a block device

Use rbd to map an image name to a kernel module. You must specify the image name, the pool name and the user name. rbd will load the RBD kernel module if it is not already loaded.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. Map an image name to a kernel module:

    Syntax

    rbd device map POOL_NAME/IMAGE_NAME --id USER_NAME

    Example

    [root@rbd-client ~]# rbd device map rbd/myimage --id admin

  2. Specify a secret when using cephx authentication by either the keyring or a file containing the secret:

    Syntax

    [root@rbd-client ~]# rbd device map POOL_NAME/IMAGE_NAME --id USER_NAME --keyring PATH_TO_KEYRING

    or

    [root@rbd-client ~]# rbd device map POOL_NAME/IMAGE_NAME --id USER_NAME --keyfile PATH_TO_FILE

3.5. Displaying mapped block devices

You can display which block device images are mapped to the kernel module with the rbd command.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. Display the mapped block devices:

    [root@rbd-client ~]# rbd device list

3.6. Unmapping a block device

You can unmap a block device image with the rbd command, by using the unmap option and providing the device name.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. Unmap the block device image:

    Syntax

    rbd device unmap /dev/rbd/POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd device unmap /dev/rbd/rbd/foo

Chapter 4. Snapshot management

As a storage administrator, being familiar with Ceph’s snapshotting feature can help you manage the snapshots and clones of images stored in the Red Hat Ceph Storage cluster.

4.1. Prerequisites

  • A running Red Hat Ceph Storage cluster.

4.2. Ceph block device snapshots

A snapshot is a read-only copy of the state of an image at a particular point in time. One of the advanced features of Ceph block devices is that you can create snapshots of the images to retain a history of an image’s state. Ceph also supports snapshot layering, which allows you to clone images quickly and easily, for example a virtual machine image. Ceph supports block device snapshots using the rbd command and many higher level interfaces, including QEMU, libvirt, OpenStack and CloudStack.

Note

If a snapshot is taken while I/O is occurring, then the snapshot might not get the exact or latest data of the image and the snapshot might have to be cloned to a new image to be mountable. Red Hat recommends stopping I/O before taking a snapshot of an image. If the image contains a filesystem, the filesystem must be in a consistent state before taking a snapshot. To stop I/O you can use fsfreeze command. For virtual machines, the qemu-guest-agent can be used to automatically freeze filesystems when creating a snapshot.

diag 4159dacfb6618377a0165242566e9e0b

Additional Resources

  • See the fsfreeze(8) man page for more details.

4.3. The Ceph user and keyring

When cephx is enabled, you must specify a user name or ID and a path to the keyring containing the corresponding key for the user.

Note

cephx is enabled by default.

You might also add the CEPH_ARGS environment variable to avoid re-entry of the following parameters:

Syntax

rbd --id USER_ID --keyring=/path/to/secret [commands]
rbd --name USERNAME --keyring=/path/to/secret [commands]

Example

[root@rbd-client ~]# rbd --id admin --keyring=/etc/ceph/ceph.keyring [commands]
[root@rbd-client ~]# rbd --name client.admin --keyring=/etc/ceph/ceph.keyring [commands]

Tip

Add the user and secret to the CEPH_ARGS environment variable so that you do not need to enter them each time.

4.4. Creating a block device snapshot

Create a snapshot of a Ceph block device.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. Specify the snap create option, the pool name and the image name:

    Syntax

    rbd --pool POOL_NAME snap create --snap SNAP_NAME IMAGE_NAME
    rbd snap create POOL_NAME/IMAGE_NAME@SNAP_NAME

    Example

    [root@rbd-client ~]# rbd --pool rbd snap create --snap snapname foo
    [root@rbd-client ~]# rbd snap create rbd/foo@snapname

4.5. Listing the block device snapshots

List the block device snapshots.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. Specify the pool name and the image name:

    Syntax

    rbd --pool POOL_NAME snap ls IMAGE_NAME
    rbd snap ls POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd --pool rbd snap ls foo
    [root@rbd-client ~]# rbd snap ls rbd/foo

4.6. Rolling back a block device snapshot

Rollback a block device snapshot.

Note

Rolling back an image to a snapshot means overwriting the current version of the image with data from a snapshot. The time it takes to execute a rollback increases with the size of the image. It is faster to clone from a snapshot than to rollback an image to a snapshot, and it is the preferred method of returning to a pre-existing state.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. Specify the snap rollback option, the pool name, the image name and the snap name:

    Syntax

    rbd --pool POOL_NAME snap rollback --snap SNAP_NAME IMAGE_NAME
    rbd snap rollback POOL_NAME/IMAGE_NAME@SNAP_NAME

    Example

    [root@rbd-client ~]# rbd --pool rbd snap rollback --snap snapname foo
    [root@rbd-client ~]# rbd snap rollback rbd/foo@snapname

4.7. Deleting a block device snapshot

Delete a snapshot for Ceph block devices.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. Specify the snap rm option, the pool name, the image name and the snapshot name:

    Syntax

    rbd --pool POOL_NAME snap rm --snap SNAP_NAME IMAGE_NAME
    rbd snap rm POOL_NAME-/IMAGE_NAME@SNAP_NAME

    Example

    [root@rbd-client ~]# rbd --pool rbd snap rm --snap snapname foo
    [root@rbd-client ~]# rbd snap rm rbd/foo@snapname

Important

If an image has any clones, the cloned images retain reference to the parent image snapshot. To delete the parent image snapshot, you must flatten the child images first.

Note

Ceph OSD daemons delete data asynchronously, so deleting a snapshot does not free up the disk space immediately.

Additional Resources

4.8. Purging the block device snapshots

Purge block device snapshots.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. Specify the snap purge option and the image name:

    Syntax

    rbd --pool POOL_NAME snap purge IMAGE_NAME
    rbd snap purge POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd --pool rbd snap purge foo
    [root@rbd-client ~]# rbd snap purge rbd/foo

4.9. Renaming a block device snapshot

Rename a block device snapshot.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. To rename a snapshot:

    Syntax

    rbd snap rename POOL_NAME/IMAGE_NAME@ORIGINAL_SNAPSHOT_NAME POOL_NAME/IMAGE_NAME@NEW_SNAPSHOT_NAME

    Example

    [root@rbd-client ~]# rbd snap rename data/dataset@snap1 data/dataset@snap2

    This renames snap1 snapshot of the dataset image on the data pool to snap2.

  2. Execute the rbd help snap rename command to display additional details on renaming snapshots.

4.10. Ceph block device layering

Ceph supports the ability to create many copy-on-write (COW) or copy-on-read (COR) clones of a block device snapshot. Snapshot layering enables Ceph block device clients to create images very quickly. For example, you might create a block device image with a Linux VM written to it. Then, snapshot the image, protect the snapshot, and create as many clones as you like. A snapshot is read-only, so cloning a snapshot simplifies semantics—​making it possible to create clones rapidly.

diag 967b328072067089c89ce979bb26daff
Note

The terms parent and child mean a Ceph block device snapshot, parent, and the corresponding image cloned from the snapshot, child. These terms are important for the command line usage below.

Each cloned image, the child, stores a reference to its parent image, which enables the cloned image to open the parent snapshot and read it. This reference is removed when the clone is flattened that is, when information from the snapshot is completely copied to the clone.

A clone of a snapshot behaves exactly like any other Ceph block device image. You can read to, write from, clone, and resize the cloned images. There are no special restrictions with cloned images. However, the clone of a snapshot refers to the snapshot, so you MUST protect the snapshot before you clone it.

A clone of a snapshot can be a copy-on-write (COW) or copy-on-read (COR) clone. Copy-on-write (COW) is always enabled for clones while copy-on-read (COR) has to be enabled explicitly. Copy-on-write (COW) copies data from the parent to the clone when it writes to an unallocated object within the clone. Copy-on-read (COR) copies data from the parent to the clone when it reads from an unallocated object within the clone. Reading data from a clone will only read data from the parent if the object does not yet exist in the clone. Rados block device breaks up large images into multiple objects. The default is set to 4 MB and all copy-on-write (COW) and copy-on-read (COR) operations occur on a full object, that is writing 1 byte to a clone will result in a 4 MB object being read from the parent and written to the clone if the destination object does not already exist in the clone from a previous COW/COR operation.

Whether or not copy-on-read (COR) is enabled, any reads that cannot be satisfied by reading an underlying object from the clone will be rerouted to the parent. Since there is practically no limit to the number of parents, meaning that you can clone a clone, this reroute continues until an object is found or you hit the base parent image. If copy-on-read (COR) is enabled, any reads that fail to be satisfied directly from the clone result in a full object read from the parent and writing that data to the clone so that future reads of the same extent can be satisfied from the clone itself without the need of reading from the parent.

This is essentially an on-demand, object-by-object flatten operation. This is specially useful when the clone is in a high-latency connection away from it’s parent, that is the parent in a different pool, in another geographical location. Copy-on-read (COR) reduces the amortized latency of reads. The first few reads will have high latency because it will result in extra data being read from the parent, for example, you read 1 byte from the clone but now 4 MB has to be read from the parent and written to the clone, but all future reads will be served from the clone itself.

To create copy-on-read (COR) clones from snapshot you have to explicitly enable this feature by adding rbd_clone_copy_on_read = true under [global] or [client] section in the ceph.conf file.

Additional Resources

  • For more information on flattening, see the Flattening cloned images section in the Red Hat Ceph Storage Block Device Gudie.

4.11. Protecting a block device snapshot

Clones access the parent snapshots. All clones would break if a user inadvertently deleted the parent snapshot. To prevent data loss, by default, you MUST protect the snapshot before you can clone it.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. Specify POOL_NAME, IMAGE_NAME, and SNAP_SHOT_NAME in the following command:

    Syntax

    rbd --pool POOL_NAME snap protect --image IMAGE_NAME --snap SNAPSHOT_NAME
    rbd snap protect POOL_NAME/IMAGE_NAME@SNAPSHOT_NAME

    Example

    [root@rbd-client ~]# rbd --pool rbd snap protect --image my-image --snap my-snapshot
    [root@rbd-client ~]# rbd snap protect rbd/my-image@my-snapshot

    Note

    You cannot delete a protected snapshot.

4.12. Cloning a block device snapshot

Clone a block device snapshot to create a read or write child image of the snapshot within the same pool or in another pool. One use case would be to maintain read-only images and snapshots as templates in one pool, and writable clones in another pool.

Important

By default, you must protect the snapshot before you can clone it. To avoid having to protect the snapshot before you clone it, set ceph osd set-require-min-compat-client mimic. You can set it to higher versions than mimic as well.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. To clone a snapshot, you need to specify the parent pool, snapshot, child pool and image name:

    Syntax

    rbd --pool POOL_NAME --image PARENT_IMAGE --snap SNAP_NAME --dest-pool POOL_NAME --dest CHILD_IMAGE_NAME
    rbd clone POOL_NAME/PARENT_IMAGE@SNAP_NAME  POOL_NAME/CHILD_IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd --pool rbd --image my-image --snap my-snapshot --dest-pool rbd --dest new-image
    [root@rbd-client ~]# rbd clone rbd/my-image@my-snapshot rbd/new-image

4.13. Unprotecting a block device snapshot

Before you can delete a snapshot, you must unprotect it first. Additionally, you may NOT delete snapshots that have references from clones. You must flatten each clone of a snapshot, before you can delete the snapshot.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. Run the following commands:

    Syntax

    rbd --pool POOL_NAME snap unprotect --image IMAGE_NAME --snap SNAPSHOT_NAME
    rbd snap unprotect POOL_NAME/IMAGE_NAME@SNAPSHOT_NAME

    Example

    [root@rbd-client ~]# rbd --pool rbd snap unprotect --image my-image --snap my-snapshot
    [root@rbd-client ~]# rbd snap unprotect rbd/my-image@my-snapshot

4.14. Listing the children of a snapshot

List the children of a snapshot.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. To list the children of a snapshot, execute the following:

    Syntax

    rbd --pool POOL_NAME children --image IMAGE_NAME --snap SNAP_NAME
    rbd children POOL_NAME/IMAGE_NAME@SNAPSHOT_NAME

    Example

    rbd --pool rbd children --image my-image --snap my-snapshot
    rbd children rbd/my-image@my-snapshot

4.15. Flattening cloned images

Cloned images retain a reference to the parent snapshot. When you remove the reference from the child clone to the parent snapshot, you effectively "flatten" the image by copying the information from the snapshot to the clone. The time it takes to flatten a clone increases with the size of the snapshot. Because a flattened image contains all the information from the snapshot, a flattened image will use more storage space than a layered clone.

Note

If the deep flatten feature is enabled on an image, the image clone is dissociated from its parent by default.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. To delete a parent image snapshot associated with child images, you must flatten the child images first:

    Syntax

    rbd --pool POOL_NAME flatten --image IMAGE_NAME
    rbd flatten POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd --pool rbd flatten --image my-image
    [root@rbd-client ~]# rbd flatten rbd/my-image

Chapter 5. Mirroring Ceph block devices

As a storage administrator, you can add another layer of redundancy to Ceph block devices by mirroring data images between Red Hat Ceph Storage clusters. Understanding and using Ceph block device mirroring can provide you protection against data loss, such as a site failure. There are two configurations for mirroring Ceph block devices, one-way mirroring or two-way mirroring, and you can configure mirroring on pools and individual images.

5.1. Prerequisites

  • A minimum of two healthy running Red Hat Ceph Storage clusters.
  • Network connectivity between the two storage clusters.
  • Access to a Ceph client node for each Red Hat Ceph Storage cluster.

5.2. Ceph block device mirroring

RADOS Block Device (RBD) mirroring is a process of asynchronous replication of Ceph block device images between two or more Ceph storage clusters. By locating a Ceph storage cluster in different geographic locations, RBD Mirroring can help you recover from a site disaster. Journal-based Ceph block device mirroring ensures point-in-time consistent replicas of all changes to an image, including reads and writes, block device resizing, snapshots, clones and flattening.

RBD mirroring uses exclusive locks and the journaling feature to record all modifications to an image in the order in which they occur. This ensures that a crash-consistent mirror of an image is available.

Important

The CRUSH hierarchies supporting primary and secondary pools that mirror block device images must have the same capacity and performance characteristics, and must have adequate bandwidth to ensure mirroring without excess latency. For example, if you have X MB/s average write throughput to images in the primary storage cluster, the network must support N * X throughput in the network connection to the secondary site plus a safety factor of Y% to mirror N images.

The rbd-mirror daemon is responsible for synchronizing images from one Ceph storage cluster to another Ceph storage cluster by pulling changes from the remote primary image and writes those changes to the local, non-primary image. The rbd-mirror daemon can run either on a single Ceph storage cluster for one-way mirroring or on two Ceph storage clusters for two-way mirroring that participate in the mirroring relationship.

For RBD mirroring to work, either using one-way or two-way replication, a couple of assumptions are made:

  • A pool with the same name exists on both storage clusters.
  • A pool contains journal-enabled images you want to mirror.
Important

In one-way or two-way replication, each instance of rbd-mirror must be able to connect to the other Ceph storage cluster simultaneously. Additionally, the network must have sufficient bandwidth between the two data center sites to handle mirroring.

One-way Replication

One-way mirroring implies that a primary image or pool of images in one storage cluster gets replicated to a secondary storage cluster. One-way mirroring also supports replicating to multiple secondary storage clusters.

On the secondary storage cluster, the image is the non-primary replicate; that is, Ceph clients cannot write to the image. When data is mirrored from a primary storage cluster to a secondary storage cluster, the rbd-mirror runs ONLY on the secondary storage cluster.

For one-way mirroring to work, a couple of assumptions are made:

  • You have two Ceph storage clusters and you want to replicate images from a primary storage cluster to a secondary storage cluster.
  • The secondary storage cluster has a Ceph client node attached to it running the rbd-mirror daemon. The rbd-mirror daemon will connect to the primary storage cluster to sync images to the secondary storage cluster.
One-way mirroring

Two-way Replication

Two-way replication adds an rbd-mirror daemon on the primary cluster so images can be demoted on it and promoted on the secondary cluster. Changes can then be made to the images on the secondary cluster and they will be replicated in the reverse direction, from secondary to primary. Both clusters must have rbd-mirror running to allow promoting and demoting images on either cluster. Currently, two-way replication is only supported between two sites.

For two-way mirroring to work, a couple of assumptions are made:

  • You have two storage clusters and you want to be able to replicate images between them in either direction.
  • Both storage clusters have a client node attached to them running the rbd-mirror daemon. The rbd-mirror daemon running on the secondary storage cluster will connect to the primary storage cluster to synchronize images to secondary, and the rbd-mirror daemon running on the primary storage cluster will connect to the secondary storage cluster to synchronize images to primary.
Two-way mirroring
Note

As of Red Hat Ceph Storage 4, running multiple active rbd-mirror daemons in a single cluster is supported.

Mirroring Modes

Mirroring is configured on a per-pool basis with mirror peering storage clusters. Ceph supports two mirroring modes, depending on the type of images in the pool.

Pool Mode
All images in a pool with the journaling feature enabled are mirrored.
Image Mode
Only a specific subset of images within a pool are mirrored. You must enable mirroring for each image separately.

Image States

Whether or not an image can be modified depends on its state:

  • Images in the primary state can be modified.
  • Images in the non-primary state cannot be modified.

Images are automatically promoted to primary when mirroring is first enabled on an image. The promotion can happen:

  • Implicitly by enabling mirroring in pool mode.
  • Explicitly by enabling mirroring of a specific image.

It is possible to demote primary images and promote non-primary images.

Additional Resources

5.3. Configuring one-way mirroring using Ansible

This procedure uses ceph-ansible to configure one-way replication of images on a primary storage cluster known as site-a, to a secondary storage cluster known as site-b. In the following examples, data is the name of the pool that contains the images to be mirrored.

Prerequisites

  • Two running Red Hat Ceph Storage clusters.
  • A Ceph client node.
  • A pool with the same name exists on both clusters.
  • Images within the pool must have exclusive-lock and journaling enabled.
Note

When using one-way replication, you can mirror to multiple secondary storage clusters.

Procedure

  1. Enable the exclusive-lock and journaling features on an image.

    1. For new images, use the --image-feature option:

      Syntax

      rbd create IMAGE_NAME --size MEGABYTES --pool POOL_NAME --image-feature FEATURE[,FEATURE]

      Example

      [root@rbd-client ~]# rbd create image1 --size 1024 --pool data --image-feature exclusive-lock,journaling

    2. For existing images, use the rbd feature enable command:

      Syntax

      rbd feature enable POOL_NAME/IMAGE_NAME FEATURE_NAME

      Example

      [root@rbd-client ~]# rbd feature enable data/image1 exclusive-lock,journaling

    3. To enable exclusive-lock and journaling on all new images by default, add the following setting to the Ceph configuration file:

      rbd_default_features = 125
  2. On the Ansible administration node of the site-b cluster, add an [rbdmirrors] group in the Ansible inventory file. The usual inventory file is /etc/ansible/hosts.
  3. Under the [rbdmirrors] group, add the name of the site-b client node on which the rbd-mirror daemon will run. The daemon will pull image changes from site-a to site-b.

    [rbdmirrors]
    ceph-client
  4. Navigate to the /usr/share/ceph-ansible/ directory:

    [root@admin ~]# cd /usr/share/ceph-ansible
  5. Create a new rbdmirrors.yml file by copying group_vars/rbdmirrors.yml.sample to group_vars/rbdmirrors.yml.

    [root@admin ceph-ansible]# cp group_vars/rbdmirrors.yml.sample group_vars/rbdmirrors.yml
  6. Open the group_vars/rbdmirrors.yml file for editing.
  7. Set ceph_rbd_mirror_configure to true. Set ceph_rbd_mirror_pool to the pool in which you want to mirror images. In these examples, data is the name of the pool.

    ceph_rbd_mirror_configure: true
    ceph_rbd_mirror_pool: "data"
  8. Optional: By default, ceph-ansible configures mirroring using pool mode which mirrors all images in a pool. It is also possible to use image mode where only images that have mirroring explicitly enabled are mirrored. To enable image mode set ceph_rbd_mirror_mode to image:

    ceph_rbd_mirror_mode: image
  9. Optional: If you set image mode, explicitly enable mirroring on the desired images:

    Syntax

    rbd mirror image enable POOL/IMAGE

    Example

    [root@mon ~]# rbd mirror image enable data/image1

  10. On a monitor node in the site-a cluster, create the user that the rbd-mirror daemon will use to connect to the cluster. The example creates a site-a user and outputs the key to a file named site-a.client.site-a.keyring:

    Syntax

    ceph auth get-or-create client.CLUSTER_NAME mon 'profile rbd' osd 'profile rbd pool=data' -o /etc/ceph/CLUSTER_NAME.client.USER_NAME.keyring

    Example

    [root@mon ~]# ceph auth get-or-create client.site-a mon 'profile rbd' osd 'profile rbd pool=data' -o /etc/ceph/site-a.client.site-a.keyring

  11. Copy the Ceph configuration file and the newly created key file from the site-a monitor node to the site-b monitor and client nodes. Rename the Ceph configuration file from ceph.conf to CLUSTER-NAME.conf. In these examples, the file is /etc/ceph/site-a.conf
  12. Set a name for the cluster that rbd-mirror will pull from. In these examples, the other cluster is site-a:

    ceph_rbd_mirror_remote_cluster: "site-a"
  13. On the Ansible administration node, set the user name of the key using ceph_rbd_mirror_remote_user. Use the same name you used when you created the key. In these examples the user is named client.site-a.

    ceph_rbd_mirror_remote_user: "client.site-a"
  14. Enable mirroring on site-a:

    Syntax

    rbd mirror pool enable pool -p POOL_NAME

    Example

    [root@mon ~]# rbd mirror pool enable pool -p data

  15. As the ceph-ansible user, run the Ansible playbook:

    • Bare-metal deployments:

      [user@admin ceph-ansible]$ ansible-playbook site.yml --limit rbdmirrors -i hosts
    • Container deployments:

      [ansible@admin ceph-ansible]$ ansible-playbook site-container.yml --limit rbdmirrors -i hosts
  16. Verify the mirroring status. Run the following command from a Ceph Monitor node in the site-b cluster:

    Example

    [root@mon ~]# rbd mirror image status data/image1
    image1:
      global_id:   7d486c3f-d5a1-4bee-ae53-6c4f1e0c8eac
      state:       up+replaying 1
      description: replaying, master_position=[object_number=3, tag_tid=1, entry_tid=3], mirror_position=[object_number=3, tag_tid=1, entry_tid=3], entries_behind_master=0
      last_update: 2019-04-22 13:19:27

    1
    If images are in the state up+replaying, then mirroring is functioning properly.
    Note

    Based on the connection between the sites, mirroring can take a long time to sync the images.

5.4. Configuring two-way mirroring using Ansible

This procedure uses ceph-ansible to configure two-way replication so images can be mirrored in either direction between two clusters known as site-a and site-b. In the following examples, data is the name of the pool that contains the images to be mirrored.

Note

Two-way mirroring does not allow simultaneous writes to be made to the same image on either cluster. Images are promoted on one cluster and demoted on another. Depending on their status, they will mirror in one direction or the other.

Prerequisites

  • Two running Red Hat Ceph Storage clusters.
  • Each cluster has a client node.
  • A pool with the same name exists on both clusters.
  • Images within the pool must have exclusive-lock and journaling enabled.

Procedure

  1. On the cluster where the images originate, enable the exclusive-lock and journaling features on an image.

    1. For new images, use the --image-feature option:

      Syntax

      rbd create IMAGE_NAME --size MEGABYTES --pool POOL_NAME --image-feature FEATURE[,FEATURE]

      Example

      [root@rbd-client ~]# rbd create image1 --size 1024 --pool data --image-feature exclusive-lock,journaling

    2. For existing images, use the rbd feature enable command:

      Syntax

      rbd feature enable POOL_NAME/IMAGE_NAME FEATURE_NAME

      Example

      [root@rbd-client ~]# rbd feature enable data/image1 exclusive-lock,journaling

    3. To enable exclusive-lock and journaling on all new images by default, add the following setting to the Ceph configuration file:

      rbd_default_features = 125
  2. Configure mirroring from site-a to site-b. On the Ansible administration node of the site-b cluster, add an [rbdmirrors] group in the Ansible inventory file, usually /usr/share/ceph-ansible/hosts.
  3. Under the [rbdmirrors] group, add the name of a site-b client node that the rbd-mirror daemon will run on. This daemon pulls image changes from site-a to site-b.

    [rbdmirrors]
    ceph-client
  4. Navigate to the /usr/share/ceph-ansible/ directory:

    [root@admin ~]$ cd /usr/share/ceph-ansible
  5. Create a new rbdmirrors.yml file by copying group_vars/rbdmirrors.yml.sample to group_vars/rbdmirrors.yml.

    [root@admin ceph-ansible]# cp group_vars/rbdmirrors.yml.sample group_vars/rbdmirrors.yml
  6. Open for editing the group_vars/rbdmirrors.yml file.
  7. Set ceph_rbd_mirror_configure to true, and set ceph_rbd_mirror_pool to the pool you want to mirror images in. In these examples, data is the name of the pool.

    ceph_rbd_mirror_configure: true
    ceph_rbd_mirror_pool: "data"
  8. Optional: By default, ceph-ansible configures mirroring using pool mode, which mirrors all images in a pool. It is also possible to use image mode where only images that have mirroring explicitly enabled are mirrored. To enable image mode, set ceph_rbd_mirror_mode to image:

    ceph_rbd_mirror_mode: image
  9. Optional: If you set image mode, explicitly enable mirroring on the desired images:

    Syntax

    rbd mirror image enable POOL/IMAGE

    Example

    [root@mon ~]# rbd mirror image enable data/image1

  10. On a monitor node in the site-a cluster, create the user the rbd-mirror daemon will use to connect to the cluster. The example creates a site-a user and outputs the key to a file named site-a.client.site-a.keyring:

    Syntax

    ceph auth get-or-create client.CLUSTER_NAME mon 'profile rbd' osd 'profile rbd pool=data' -o /etc/ceph/CLUSTER_NAME.client.USER_NAME.keyring

    Example

    [root@mon ~]# ceph auth get-or-create client.site-a mon 'profile rbd' osd 'profile rbd pool=data' -o /etc/ceph/site-a.client.site-a.keyring

  11. Copy the Ceph configuration file and the newly created key file from the site-a monitor node to the site-b monitor and client nodes. Rename the Ceph configuration file from ceph.conf to CLUSTER-NAME.conf. In these examples, the file is /etc/ceph/site-a.conf
  12. Set a name for the cluster that rbd-mirror will pull from. In these examples, the other cluster is site-a:

    ceph_rbd_mirror_remote_cluster: "site-a"
  13. On the Ansible administration node, set the user name of the key using ceph_rbd_mirror_remote_user. Use the same name you used when you created the key. In these examples the user is named client.site-a.

    ceph_rbd_mirror_remote_user: "client.site-a"
  14. As the ansible user, run the Ansible playbook:

    • Bare-metal deployments:

      [user@admin ceph-ansible]$ ansible-playbook site.yml --limit rbdmirrors -i hosts
    • Container deployments:

      [user@admin ceph-ansible]$ ansible-playbook site-container.yml --limit rbdmirrors -i hosts
  15. Verify the mirroring status. Run the following command from a Ceph Monitor node on the site-b cluster:

    Example

    [root@mon ~]# rbd mirror image status data/image1
    image1:
      global_id:   7d486c3f-d5a1-4bee-ae53-6c4f1e0c8eac
      state:       up+replaying 1
      description: replaying, master_position=[object_number=3, tag_tid=1, entry_tid=3], mirror_position=[object_number=3, tag_tid=1, entry_tid=3], entries_behind_master=0
      last_update: 2019-04-22 13:19:27

    1
    If images are in the state up+replaying, then mirroring is functioning properly.
    Note

    Based on the connection between the sites, mirroring can take a long time to sync the images.

  16. Configure mirroring from site-b to site-a. The steps are largely the same as above. On the Ansible administration node of the site-a cluster, add an [rbdmirrors] group in the Ansible inventory file, usually /usr/share/ceph-ansible/hosts.
  17. Under the [rbdmirrors] group, add the name of a site-a client node that the rbd-mirror daemon will run on. This daemon pulls image changes from site-b to site-a.

    [rbdmirrors]
    ceph-client
  18. Navigate to the /usr/share/ceph-ansible/ directory:

    [root@admin ~]# cd /usr/share/ceph-ansible
  19. Create a new rbdmirrors.yml file by copying group_vars/rbdmirrors.yml.sample to group_vars/rbdmirrors.yml.

    [root@admin ceph-ansible]# cp group_vars/rbdmirrors.yml.sample group_vars/rbdmirrors.yml
  20. Open for editing the group_vars/rbdmirrors.yml file.
  21. Set ceph_rbd_mirror_configure to true, and set ceph_rbd_mirror_pool to the pool you want to mirror images in. In these examples, data is the name of the pool.

    ceph_rbd_mirror_configure: true
    ceph_rbd_mirror_pool: "data"
  22. Optional: By default, ceph-ansible configures mirroring using pool mode which mirrors all images in a pool. It is also possible to use image mode where only images that have mirroring explicitly enabled are mirrored. To enable image mode set ceph_rbd_mirror_mode to image:

    ceph_rbd_mirror_mode: image
  23. Optional: If you set image mode, explicitly enable mirroring on the desired images:

    Syntax

    rbd mirror image enable POOL/IMAGE

    Example

    [root@mon ~]# rbd mirror image enable data/image1

  24. Copy the RBD key from the site-b cluster to the site-a cluster. The key is on the client node you configured the rbd-mirror daemon to run on in step three. The file is in the /etc/ceph/ directory and has rbd-mirror in the name and ends in the .keyring extension. Copy the file to the client node in the site-a cluster that the rbd-daemon will run on. Following the examples, save the file to /etc/ceph/site-b.client.site-b.keyring
  25. Copy the Ceph configuration file from the site-b cluster to the client node in the site-a cluster that the rbd-daemon will run on. Following the examples, save the file to /etc/ceph/site-b.conf.
  26. On the Ansible administration node on the site-a cluster, set a name for the cluster that rbd-mirror will pull from. Following the examples, the other cluster is named site-b:

    ceph_rbd_mirror_remote_cluster: "site-b"
  27. On the Ansible administration node on the site-a cluster, set the user name of the key using ceph_rbd_mirror_remote_user in group_vars/rbdmirrors.yml. In these examples the user is named client.site-b.

    ceph_rbd_mirror_remote_user: "client.site-b"
  28. As the Ansible user on the administration node of the site-a cluster, run the Ansible playbook:

    • Bare-metal deployments:

      [user@admin ceph-ansible]$ ansible-playbook site.yml --limit rbdmirrors -i hosts
    • Container deployments:

      [user@admin ceph-ansible]$ ansible-playbook site-container.yml --limit rbdmirrors -i hosts
  29. Check the mirroring status from the client node on the site-a cluster.

    [root@mon ~]# rbd mirror image status data/image1
    image1:
      global_id:   08027096-d267-47f8-b52e-59de1353a034
      state:       up+stopped
      description: local image is primary
      last_update: 2019-04-16 15:45:31
    [root@mon ~]# rbd mirror image status data/image2
    image1:
      global_id:   596f41bc-874b-4cd4-aefe-4929578cc834
      state:       up+stopped
      description: local image is primary
      last_update: 2019-04-16 15:55:33

    The images should be in state up+stopped. Here, up means the rbd-mirror daemon is running and stopped means the image is not a target for replication from another cluster. This is because the images are primary on this cluster.

5.5. Configuring one-way mirroring using the command-line interface

This procedure configures one-way replication of a pool from the primary storage cluster to a secondary storage cluster.

Note

When using one-way replication you can mirror to multiple secondary storage clusters.

Note

Examples in this section will distinguish between two storage clusters by referring to the primary storage cluster with the primary images as site-a, and the secondary storage cluster you are replicating the images to, as site-b. The pool name used in these examples is called data.

Prerequisites

  • A minimum of two healthy and running Red Hat Ceph Storage clusters.
  • Root-level access to a Ceph client node for each storage cluster.
  • A CephX user with administrator-level capabilities.
  • Images within the pool must have exclusive-lock and journaling enabled.

Procedure

  1. Install the rbd-mirror package on the client node connected to the site-b storage cluster:

    Red Hat Enterprise Linux 7

    [root@rbd-client ~]# yum install rbd-mirror

    Red Hat Enterprise Linux 8

    [root@rbd-client ~]# dnf install rbd-mirror

    Note

    The package is provided by the Red Hat Ceph Storage Tools repository.

  2. Enable the exclusive-lock, and journaling features on an image.

    1. For new images, use the --image-feature option:

      Syntax

      rbd create IMAGE_NAME --size MEGABYTES --pool POOL_NAME --image-feature FEATURE [,FEATURE]

      Example

      [root@rbd-client ~]# rbd create image1 --size 1024 --pool data --image-feature exclusive-lock,journaling

    2. For existing images, use the rbd feature enable command:

      Syntax

      rbd feature enable POOL_NAME/IMAGE_NAME FEATURE [,FEATURE]

      Example

      [root@rbd-client ~]# rbd feature enable data/image1 exclusive-lock,journaling

    3. To enable exclusive-lock and journaling on all new images by default, add the following setting to the Ceph configuration file:

      rbd_default_features = 125
  3. Choose the mirroring mode, either pool or image mode.

    1. Enabling pool mode:

      Syntax

      rbd mirror pool enable POOL_NAME MODE

      Example

      [root@rbd-client ~]# rbd mirror pool enable data pool

      This example enables mirroring of the whole pool named data.

    2. Enabling image mode:

      Syntax

      rbd mirror pool enable POOL_NAME MODE

      Example

      [root@rbd-client ~]# rbd mirror pool enable data image

      This example enables image mode mirroring on the pool named data.

    3. Verify that mirroring has been successfully enabled:

      Syntax

      rbd mirror pool info POOL_NAME

      Example

      [root@rbd-client ~]# rbd mirror pool info data
      Mode: pool
      Peers: none

  4. On the Ceph client node, create a user:

    Syntax

    ceph auth get-or-create client.PRIMARY_CLUSTER_NAME mon 'profile rbd-mirror' osd 'profile rbd' -o /etc/ceph/ceph.PRIMARY_CLUSTER_NAME.keyring

    Example

    [root@rbd-client-site-a ~]# ceph auth get-or-create client.rbd-mirror.site-a mon 'profile rbd-mirror' osd 'profile rbd' -o /etc/ceph/ceph.client.rbd-mirror.site-a.keyring

  5. Copy keyring to secondary cluster:

    Syntax

    scp /etc/ceph/ceph.PRIMARY_CLUSTER_NAME.keyring root@SECONDARY_CLUSTER:_PATH_

    Example

    [root@rbd-client-site-a ~]# scp /etc/ceph/ceph.client.rbd-mirror.site-a.keyring root@rbd-client-site-b:/etc/ceph/

  6. On a Ceph client node, bootstrap the storage cluster peers.

    1. Register the storage cluster peer to the pool:

      Syntax

      rbd mirror pool peer bootstrap create --site-name LOCAL_SITE_NAME POOL_NAME > PATH_TO_BOOTSTRAP_TOKEN

      Example

      [root@rbd-client-site-a ~]# rbd mirror pool peer bootstrap create --site-name rbd-mirror.site-a data > /root/bootstrap_token_rbd-mirror.site-a

      Note

      This example bootstrap command creates the client.rbd-mirror-peer Ceph user.

    2. Copy the bootstrap token file to the site-b storage cluster.

      Syntax

      scp PATH_TO_BOOTSTRAP_TOKEN root@SECONDARY_CLUSTER:/root/

      Example

      [root@rbd-client-site-a ~]# scp /root/bootstrap_token_site-a root@ceph-rbd2:/root/

  7. Create a user on the secondary client node:

    Syntax

    ceph auth get-or-create client.SECONDARY_CLUSTER_NAME mon 'profile rbd-mirror' osd 'profile rbd' -o /etc/ceph/ceph.SECONDARY_CLUSTER_NAME.keyring

    Example

    [root@rbd-client-site-b ~]# ceph auth get-or-create client.rbd-mirror.site-b mon 'profile rbd-mirror' osd 'profile rbd' -o /etc/ceph/ceph.client.rbd-mirror.site-b.keyring

  8. Copy keyring to primary cluster, the ceph client node:

    Syntax

    scp /etc/ceph/ceph.SECONDARY_CLUSTER_NAME.keyring root@PRIMARY_CLUSTER:_PATH_

    Example

    [root@rbd-client-site-b ~]# scp /etc/ceph/ceph.client.rbd-mirror.site-b.keyring root@rbd-client-site-a:/etc/ceph/

  9. Import the bootstrap token on the site-b storage cluster:

    Syntax

    rbd mirror pool peer bootstrap import --site-name LOCAL_SITE_NAME --direction rx-only POOL_NAME PATH_TO_BOOTSTRAP_TOKEN

    Example

    [root@rbd-client-site-b ~]# rbd mirror pool peer bootstrap import --site-name rbd-mirror.site-b --direction rx-only data /root/bootstrap_token_rbd-mirror.site-a

    Note

    For one-way RBD mirroring, you must use the --direction rx-only argument, as two-way mirroring is the default when bootstrapping peers.

  10. Enable and start the rbd-mirror daemon on the secondary client node:

    Syntax

    systemctl enable ceph-rbd-mirror.target
    systemctl enable ceph-rbd-mirror@rbd-mirror.CLIENT_ID
    systemctl start ceph-rbd-mirror@rbd-mirror.CLIENT_ID

    Replace CLIENT_ID with the Ceph user created earlier.

    Example

    [root@rbd-client-site-b ~]# systemctl enable ceph-rbd-mirror.target
    [root@rbd-client-site-b ~]# systemctl enable ceph-rbd-mirror@rbd-mirror.site-a
    [root@rbd-client-site-b ~]# systemctl start ceph-rbd-mirror@rbd-mirror.site-a

    Important

    Each rbd-mirror daemon must have a unique client id.

  11. To verify the mirroring status, run the following command from a Ceph Monitor node on the primary and secondary sites:

    Syntax

    rbd mirror image status POOL_NAME/IMAGE_NAME

    Example

    [root@mon-site-a ~]# rbd mirror image status data/image1
    image1:
      global_id:   08027096-d267-47f8-b52e-59de1353a034
      state:       up+stopped 1
      description: local image is primary
      last_update: 2021-04-22 13:45:31

    1
    Here, up means the rbd-mirror daemon is running, and stopped means this image is not the target for replication from another storage cluster. This is because the image is primary on this storage cluster.

    Example

    [root@mon-site-b ~]# rbd mirror image status data/image1
    image1:
      global_id:   7d486c3f-d5a1-4bee-ae53-6c4f1e0c8eac
      state:       up+replaying 1
      description: replaying, master_position=[object_number=3, tag_tid=1, entry_tid=3], mirror_position=[object_number=3, tag_tid=1, entry_tid=3], entries_behind_master=0
      last_update: 2021-04-22 14:19:27

    1
    If images are in the state up+replaying, then mirroring is functioning properly. Here, up means the rbd-mirror daemon is running, and replaying means this image is the target for replication from another storage cluster.
    Note

    Depending on the connection between the sites, mirroring can take a long time to sync the images.

Additional Resources

  • See the Ceph block device mirroring section in the Red Hat Ceph Storage Block Device Guide for more details.
  • See the User Management section in the Red Hat Ceph Storage Administration Guide for more details on Ceph users.

5.6. Configuring two-way mirroring using the command-line interface

This procedure configures two-way replication of a pool between the primary storage cluster, and a secondary storage cluster.

Note

When using two-way replication you can only mirror between two storage clusters.

Note

Examples in this section will distinguish between two storage clusters by referring to the primary storage cluster with the primary images as site-a, and the secondary storage cluster you are replicating the images to, as site-b. The pool name used in these examples is called data.

Prerequisites

  • A minimum of two healthy and running Red Hat Ceph Storage clusters.
  • Root-level access to a Ceph client node for each storage cluster.
  • A CephX user with administrator-level capabilities.
  • Images within the pool must have exclusive-lock and journaling enabled.

Procedure

  1. Install the rbd-mirror package on the client node connected to the site-a storage cluster, and the client node connected to the site-b storage cluster:

    Red Hat Enterprise Linux 7

    [root@rbd-client ~]# yum install rbd-mirror

    Red Hat Enterprise Linux 8

    [root@rbd-client ~]# dnf install rbd-mirror

    Note

    The package is provided by the Red Hat Ceph Storage Tools repository.

  2. Enable the exclusive-lock, and journaling features on an image.

    1. For new images, use the --image-feature option:

      Syntax

      rbd create IMAGE_NAME --size MEGABYTES --pool POOL_NAME --image-feature FEATURE [,FEATURE]

      Example

      [root@rbd-client ~]# rbd create image1 --size 1024 --pool data --image-feature exclusive-lock,journaling

    2. For existing images, use the rbd feature enable command:

      Syntax

      rbd feature enable POOL_NAME/IMAGE_NAME FEATURE [,FEATURE]

      Example

      [root@rbd-client ~]# rbd feature enable data/image1 exclusive-lock,journaling

    3. To enable exclusive-lock and journaling on all new images by default, add the following setting to the Ceph configuration file:

      rbd_default_features = 125
  3. Choose the mirroring mode, either pool or image mode.

    1. Enabling pool mode:

      Syntax

      rbd mirror pool enable POOL_NAME MODE

      Example

      [root@rbd-client ~]# rbd mirror pool enable data pool

      This example enables mirroring of the whole pool named data.

    2. Enabling image mode:

      Syntax

      rbd mirror pool enable POOL_NAME MODE

      Example

      [root@rbd-client ~]# rbd mirror pool enable data image

      This example enables image mode mirroring on the pool named data.

    3. Verify that mirroring has been successfully enabled:

      Syntax

      rbd mirror pool info POOL_NAME

      Example

      [root@rbd-client ~]# rbd mirror pool info data
      Mode: pool
      Peers: none

  4. On the Ceph client node, create a user:

    Syntax

    ceph auth get-or-create client.PRIMARY_CLUSTER_NAME mon 'profile rbd-mirror' osd 'profile rbd' -o /etc/ceph/ceph.PRIMARY_CLUSTER_NAME.keyring

    Example

    [root@rbd-client-site-a ~]# ceph auth get-or-create client.rbd-mirror.site-a mon 'profile rbd-mirror' osd 'profile rbd' -o /etc/ceph/ceph.client.rbd-mirror.site-a.keyring

  5. Copy keyring to secondary cluster:

    Syntax

    scp /etc/ceph/ceph.PRIMARY_CLUSTER_NAME.keyring root@SECONDARY_CLUSTER:_PATH_

    Example

    [root@rbd-client-site-a ~]# scp /etc/ceph/ceph.client.rbd-mirror.site-a.keyring root@rbd-client-site-b:/etc/ceph/

  6. On a Ceph client node, bootstrap the storage cluster peers.

    1. Register the storage cluster peer to the pool:

      Syntax

      rbd mirror pool peer bootstrap create --site-name LOCAL_SITE_NAME POOL_NAME > PATH_TO_BOOTSTRAP_TOKEN

      Example

      [root@rbd-client-site-a ~]# rbd mirror pool peer bootstrap create --site-name rbd-mirror.site-a data > /root/bootstrap_token_rbd-mirror.site-a

      Note

      This example bootstrap command creates the client.rbd-mirror-peer Ceph user.

    2. Copy the bootstrap token file to the site-b storage cluster.

      Syntax

      scp PATH_TO_BOOTSTRAP_TOKEN root@SECONDARY_CLUSTER:/root/

      Example

      [root@rbd-client-site-a ~]# scp /root/bootstrap_token_site-a root@ceph-rbd2:/root/

  7. Create a user on the secondary client node:

    Syntax

    ceph auth get-or-create client.SECONDARY_CLUSTER_NAME mon 'profile rbd-mirror' osd 'profile rbd' -o /etc/ceph/ceph.SECONDARY_CLUSTER_NAME.keyring

    Example

    [root@rbd-client-site-b ~]# ceph auth get-or-create client.rbd-mirror.site-b mon 'profile rbd-mirror' osd 'profile rbd' -o /etc/ceph/ceph.client.rbd-mirror.site-b.keyring

  8. Copy keyring to primary cluster, the ceph client node:

    Syntax

    scp /etc/ceph/ceph.SECONDARY_CLUSTER_NAME.keyring root@PRIMARY_CLUSTER:_PATH_

    Example

    [root@rbd-client-site-b ~]# scp /etc/ceph/ceph.client.rbd-mirror.site-b.keyring root@rbd-client-site-a:/etc/ceph/

  9. Import the bootstrap token on the site-b storage cluster:

    Syntax

    rbd mirror pool peer bootstrap import --site-name LOCAL_SITE_NAME --direction rx-tx POOL_NAME PATH_TO_BOOTSTRAP_TOKEN

    Example

    [root@rbd-client-site-b ~]# rbd mirror pool peer bootstrap import --site-name rbd-mirror.site-b --direction rx-tx data /root/bootstrap_token_rbd-mirror.site-a

    Note

    The --direction argument is optional, as two-way mirroring is the default when bootstrapping peers.

  10. Enable and start the rbd-mirror daemon on the primary and secondary client nodes:

    Syntax

    systemctl enable ceph-rbd-mirror.target
    systemctl enable ceph-rbd-mirror@rbd-mirror.CLIENT_ID
    systemctl start ceph-rbd-mirror@rbd-mirror.CLIENT_ID

    Replace CLIENT_ID with the Ceph user created earlier.

    Example

    [root@rbd-client-site-a ~]# systemctl enable ceph-rbd-mirror.target
    [root@rbd-client-site-a ~]# systemctl enable ceph-rbd-mirror@rbd-mirror.site-a
    [root@rbd-client-site-a ~]# systemctl start ceph-rbd-mirror@rbd-mirror.site-a
    [root@rbd-client-site-a ~]# systemctl enable ceph-rbd-mirror@rbd-mirror.site-b
    [root@rbd-client-site-a ~]# systemctl start ceph-rbd-mirror@rbd-mirror.site-b

    In the above example, users are enabled in the primary cluster site-a

    Example

    [root@rbd-client-site-b ~]# systemctl enable ceph-rbd-mirror.target
    [root@rbd-client-site-b ~]# systemctl enable ceph-rbd-mirror@rbd-mirror.site-a
    [root@rbd-client-site-b ~]# systemctl start ceph-rbd-mirror@rbd-mirror.site-a
    [root@rbd-client-site-b ~]# systemctl enable ceph-rbd-mirror@rbd-mirror.site-b
    [root@rbd-client-site-b ~]# systemctl start ceph-rbd-mirror@rbd-mirror.site-b

    In the above example, users are enabled in the secondary cluster site-b

    Important

    Each rbd-mirror daemon must have a unique client id.

  11. To verify the mirroring status, run the following command from a Ceph Monitor node on the primary and secondary sites:

    Syntax

    rbd mirror image status POOL_NAME/IMAGE_NAME

    Example

    [root@mon-site-a ~]# rbd mirror image status data/image1
    image1:
      global_id:   08027096-d267-47f8-b52e-59de1353a034
      state:       up+stopped 1
      description: local image is primary
      last_update: 2021-04-22 13:45:31

    1
    Here, up means the rbd-mirror daemon is running, and stopped means this image is not the target for replication from another storage cluster. This is because the image is primary on this storage cluster.

    Example

    [root@mon-site-b ~]# rbd mirror image status data/image1
    image1:
      global_id:   7d486c3f-d5a1-4bee-ae53-6c4f1e0c8eac
      state:       up+replaying 1
      description: replaying, master_position=[object_number=3, tag_tid=1, entry_tid=3], mirror_position=[object_number=3, tag_tid=1, entry_tid=3], entries_behind_master=0
      last_update: 2021-04-22 14:19:27

    1
    If images are in the state up+replaying, then mirroring is functioning properly. Here, up means the rbd-mirror daemon is running, and replaying means this image is the target for replication from another storage cluster.
    Note

    Depending on the connection between the sites, mirroring can take a long time to sync the images.

Additional Resources

  • See the Ceph block device mirroring section in the Red Hat Ceph Storage Block Device Guide for more details.
  • See the User Management section in the Red Hat Ceph Storage Administration Guide for more details on Ceph users.

5.7. Administration for mirroring Ceph block devices

As a storage administrator, you can do various tasks to help you manage the Ceph block device mirroring environment. You can do the following tasks:

  • Viewing information about storage cluster peers.
  • Add or remove a storage cluster peer.
  • Getting mirroring status for a pool or image.
  • Enabling mirroring on a pool or image.
  • Disabling mirroring on a pool or image.
  • Delaying block device replication.
  • Promoting and demoting an image.

5.7.1. Prerequisites

  • A minimum of two healthy running Red Hat Ceph Storage cluster.
  • Root-level access to the Ceph client nodes.
  • A one-way or two-way Ceph block device mirroring relationship.

5.7.2. Viewing information about peers

View information about storage cluster peers.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. To view information about the peers:

    Syntax

    rbd mirror pool info POOL_NAME

    Example

    [root@rbd-client ~]# rbd mirror pool info data
    Mode: pool
    Peers:
      UUID                                 NAME   CLIENT
      7e90b4ce-e36d-4f07-8cbc-42050896825d site-a client.site-a

5.7.3. Enabling mirroring on a pool

Enable mirroring on a pool by running the following commands on both peer clusters.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. To enable mirroring on a pool:

    Syntax

    rbd mirror pool enable POOL_NAME MODE

    Example

    [root@rbd-client ~]# rbd mirror pool enable data pool

    This example enables mirroring of the whole pool named data.

    Example

    [root@rbd-client ~]# rbd mirror pool enable data image

    This example enables image mode mirroring on the pool named data.

Additional Resources

5.7.4. Disabling mirroring on a pool

Before disabling mirroring, remove the peer clusters.

Note

When you disable mirroring on a pool, you also disable it on any images within the pool for which mirroring was enabled separately in image mode.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. To disable mirroring on a pool:

    Syntax

    rbd mirror pool disable POOL_NAME

    Example

    [root@rbd-client ~]# rbd mirror pool disable data

    This example disables mirroring of a pool named data.

Additional Resources

5.7.5. Enabling image mirroring

Enable mirroring on the whole pool in image mode on both peer storage clusters.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. Enable mirroring for a specific image within the pool:

    Syntax

    rbd mirror image enable POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd mirror image enable data/image2

    This example enables mirroring for the image2 image in the data pool.

Additional Resources

5.7.6. Disabling image mirroring

Disable the mirror for images.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. To disable mirroring for a specific image:

    Syntax

    rbd mirror image disable POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd mirror image disable data/image2

    This example disables mirroring of the image2 image in the data pool.

5.7.7. Image promotion and demotion

Promote or demote an image.

Note

Do not force promote non-primary images that are still syncing, because the images will not be valid after the promotion.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. To demote an image to non-primary:

    Syntax

    rbd mirror image demote POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd mirror image demote data/image2

    This example demotes the image2 image in the data pool.

  2. To promote an image to primary:

    Syntax

    rbd mirror image promote POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd mirror image promote data/image2

    This example promotes image2 in the data pool.

    Depending on which type of mirroring you are using, see either Recovering from a disaster with one-way mirroring or Recovering from a disaster with two-way mirroring for details.

  3. Use the --force option to force promote a non-primary image:

    Syntax

    rbd mirror image promote --force POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd mirror image promote --force data/image2

    Use forced promotion when the demotion cannot be propagated to the peer Ceph storage cluster. For example, because of cluster failure or communication outage.

Additional Resources

5.7.8. Image resynchronization

Re-synchronize an image. In case of an inconsistent state between the two peer clusters, the rbd-mirror daemon does not attempt to mirror the image that is causing the inconsistency.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. To request a resynchronization to the primary image:

    Syntax

    rbd mirror image resync POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd mirror image resync data/image2

    This example requests resynchronization of image2 in the data pool.

Additional Resources

5.7.9. Adding a storage cluster peer

Add a storage cluster peer for the rbd-mirror daemon to discover its peer storage cluster. For example, to add the site-a storage cluster as a peer to the site-b storage cluster, then follow this procedure from the client node in the site-b storage cluster.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. Register the peer to the pool:

    Syntax

    rbd --cluster CLUSTER_NAME mirror pool peer add POOL_NAME PEER_CLIENT_NAME@PEER_CLUSTER_NAME -n CLIENT_NAME

    Example

    [root@rbd-client ~]# rbd --cluster site-b mirror pool peer add data client.site-a@site-a -n client.site-b

5.7.10. Removing a storage cluster peer

Remove a storage cluster peer by specifying the peer UUID.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. Specify the pool name and the peer Universally Unique Identifier (UUID).

    Syntax

    rbd mirror pool peer remove POOL_NAME PEER_UUID

    Example

    [root@rbd-client ~]# rbd mirror pool peer remove data 7e90b4ce-e36d-4f07-8cbc-42050896825d

    Tip

    To view the peer UUID, use the rbd mirror pool info command.

5.7.11. Getting mirroring status for a pool

Get the mirror status for a pool.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. To get the mirroring pool summary:

    Syntax

    rbd mirror pool status POOL_NAME

    Example

    [root@rbd-client ~]# rbd mirror pool status data
    health: OK
    images: 1 total

    Tip

    To output status details for every mirroring image in a pool, use the --verbose option.

5.7.12. Getting mirroring status for a single image

Get the mirror status for an image.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. To get the status of a mirrored image:

    Syntax

    rbd mirror image status POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd mirror image status data/image2
    image2:
      global_id:   703c4082-100d-44be-a54a-52e6052435a5
      state:       up+replaying
      description: replaying, master_position=[object_number=0, tag_tid=3, entry_tid=0], mirror_position=[object_number=0, tag_tid=3, entry_tid=0], entries_behind_master=0
      last_update: 2019-04-23 13:39:15

    This example gets the status of the image2 image in the data pool.

5.7.13. Delaying block device replication

Whether you are using one- or two-way replication, you can delay replication between RADOS Block Device (RBD) mirroring images. You might want to implement delayed replication if you want a window of cushion time in case an unwanted change to the primary image needs to be reverted before being replicated to the secondary image.

To implement delayed replication, the rbd-mirror daemon within the destination storage cluster should set the rbd_mirroring_replay_delay = MINIMUM_DELAY_IN_SECONDS configuration option. This setting can either be applied globally within the ceph.conf file utilized by the rbd-mirror daemons, or on an individual image basis.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. To utilize delayed replication for a specific image, on the primary image, run the following rbd CLI command:

    Syntax

    rbd image-meta set POOL_NAME/IMAGE_NAME conf_rbd_mirroring_replay_delay MINIMUM_DELAY_IN_SECONDS

    Example

    [root@rbd-client ~]# rbd image-meta set vms/vm-1 conf_rbd_mirroring_replay_delay 600

    This example sets a 10 minute minimum replication delay on image vm-1 in the vms pool.

5.7.14. Asynchronous updates and Ceph block device mirroring

When updating a storage cluster using Ceph block device mirroring with an asynchronous update, follow the update instruction in the Red Hat Ceph Storage Installation Guide. Once updating is done, restart the Ceph block device instances.

Note

There is no required order for restarting the instances. Red Hat recommends restarting the instance pointing to the pool with primary images followed by the instance pointing to the mirrored pool.

5.7.15. Creating an image mirror-snapshot

Create an image mirror-snapshot when it is required to mirror the changed contents of an RBD image when using snapshot-based mirroring.

Prerequisites

  • A minimum of two healthy running Red Hat Ceph Storage clusters.
  • Root-level access to the Ceph client nodes for the Red Hat Ceph Storage clusters.
  • A CephX user with administrator-level capabilities.
  • Access to the Red Hat Ceph Storage cluster where a snapshot mirror will be created.
Important

By default only 3 image mirror-snapshots can be created per image. The most recent image mirror-snapshot is automatically removed if the limit is reached. If required, the limit can be overridden through the rbd_mirroring_max_mirroring_snapshots configuration. Image mirror-snapshots are automatically deleted when the image is removed or when mirroring is disabled.

Procedure

  1. To create an image-mirror snapshot:

    Syntax

    rbd --cluster CLUSTER_NAME mirror image snapshot POOL_NAME/IMAGE_NAME

    Example

    root@rbd-client ~]# rbd --cluster site-a mirror image snapshot data/image1

Additional Resources

5.7.16. Scheduling mirror-snapshots

Mirror-snapshots can be automatically created when mirror-snapshot schedules are defined. The mirror-snapshot can be scheduled globally, per-pool or per-image levels. Multiple mirror-snapshot schedules can be defined at any level but only the most specific snapshot schedules that match an individual mirrored image will run.

Additional Resources

5.7.17. Creating a mirror-snapshot schedule

Create a mirror-snapshot schedule.

Prerequisites

  • A minimum of two healthy running Red Hat Ceph Storage clusters.
  • Root-level access to the Ceph client nodes for the Red Hat Ceph Storage clusters.
  • A CephX user with administrator-level capabilities.
  • Access to the Red Hat Ceph Storage cluster where a snapshot mirror will be created.

Procedure

  1. To create a mirror-snapshot schedule:

    Syntax

    rbd --cluster CLUSTER_NAME mirror snapshot schedule add POOL_NAME/IMAGE_NAME INTERVAL START_TIME

    The interval can be specified in days, hours, or minutes using d, h, or m suffix respectively. The optional START_TIME can be specified using the ISO 8601 time format.

    Example

    [root@rbd-client ~]# rbd --cluster site-a mirror snapshot schedule add data/image1 6h

    Example

    [root@rbd-client ~]# rbd --cluster site-a mirror snapshot schedule add data/image1 24h 14:00:00-05:00

Additional Resources

5.7.18. Listing all snapshot schedules at a specific level

List all snapshot schedules at a specific level.

Prerequisites

  • A minimum of two healthy running Red Hat Ceph Storage clusters.
  • Root-level access to the Ceph client nodes for the Red Hat Ceph Storage clusters.
  • A CephX user with administrator-level capabilities.
  • Access to the Red Hat Ceph Storage cluster where a snapshot mirror will be created.

Procedure

  1. To list all snapshot schedules for a specific global, pool or image level, with an optional pool or image name:

    Syntax

    rbd --cluster site-a mirror snapshot schedule ls --pool POOL_NAME --recursive

    Additionally, the `--recursive option can be specified to list all schedules at the specified level as shown below:

    Example

    [root@rbd-client ~]# rbd --cluster site-a mirror snapshot schedule ls --pool data --recursive
    POOL        NAMESPACE IMAGE  SCHEDULE
    data         -         -      every 1d starting at 14:00:00-05:00
    data         -        image1   every 6h

Additional Resources

5.7.19. Removing a mirror-snapshot schedule

Remove a mirror-snapshot schedule.

Prerequisites

  • A minimum of two healthy running Red Hat Ceph Storage clusters.
  • Root-level access to the Ceph client nodes for the Red Hat Ceph Storage clusters.
  • A CephX user with administrator-level capabilities.
  • Access to the Red Hat Ceph Storage cluster where a snapshot mirror will be created.

Procedure

  1. To remove a mirror-snapshot schedule:

    Syntax

    rbd --cluster CLUSTER_NAME mirror snapshot schedule remove POOL_NAME/IMAGE_NAME INTERVAL START_TIME

    The interval can be specified in days, hours, or minutes using d, h, m suffix respectively. The optional START_TIME can be specified using the ISO 8601 time format.

    Example

    [root@rbd-client ~]# rbd --cluster site-a mirror snapshot schedule remove data/image1 6h

    Example

    [root@rbd-client ~]# rbd --cluster site-a mirror snapshot schedule remove data/image1 24h 14:00:00-05:00

Additional Resources

5.7.20. Viewing the status for the next snapshots to be created

View the status for the next snapshots to be created for snapshot-based mirroring RBD images.

Prerequisites

  • A minimum of two healthy running Red Hat Ceph Storage clusters.
  • Root-level access to the Ceph client nodes for the Red Hat Ceph Storage clusters.
  • A CephX user with administrator-level capabilities.
  • Access to the Red Hat Ceph Storage cluster where a snapshot mirror will be created.

Procedure

  1. To view the status for the next snapshots to be created:

    Syntax

    rbd --cluster site-a mirror snapshot schedule status POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd --cluster site-a mirror snapshot schedule status
    SCHEDULE    TIME       IMAGE
    2020-02-26 18:00:00 data/image1

Additional Resources

5.8. Recover from a disaster

As a storage administrator, you can be prepared for eventual hardware failure by knowing how to recover the data from another storage cluster where mirroring was configured.

In the examples, the primary storage cluster is known as the site-a, and the secondary storage cluster is known as the site-b. Additionally, the storage clusters both have a data pool with two images, image1 and image2.

5.8.1. Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • One-way or two-way mirroring was configured.

5.8.2. Disaster recovery

Asynchronous replication of block data between two or more Red Hat Ceph Storage clusters reduces downtime and prevents data loss in the event of a significant data center failure. These failures have a widespread impact, also referred as a large blast radius, and can be caused by impacts to the power grid and natural disasters.

Customer data needs to be protected during these scenarios. Volumes must be replicated with consistency and efficiency and also within Recovery Point Objective (RPO) and Recovery Time Objective (RTO) targets. This solution is called a Wide Area Network- Disaster Recovery (WAN-DR).

In such scenarios it is hard to restore the primary system and the data center. The quickest way to recover is to failover the applications to an alternate Red Hat Ceph Storage cluster (disaster recovery site) and make the cluster operational with the latest copy of the data available. The solutions that are used to recover from these failure scenarios are guided by the application:

  • Recovery Point Objective (RPO): The amount of data loss, an application tolerate in the worst case.
  • Recovery Time Objective (RTO): The time taken to get the application back on line with the latest copy of the data available.

Additional Resources

  • See the Mirroring Ceph block devices section in the Red Hat Ceph Storage Block Device Guide for details.
  • See the Encryption in transit section in the Red Hat Ceph Storage Data Security and Hardening Guide to know more about data transmission over the wire in an encrypted state.

5.8.3. Recover from a disaster with one-way mirroring

To recover from a disaster when using one-way mirroring use the following procedures. They show how to fail over to the secondary cluster after the primary cluster terminates, and how to fail back. The shutdown can be orderly or non-orderly.

Important

One-way mirroring supports multiple secondary sites. If you are using additional secondary clusters, choose one of the secondary clusters to fail over to. Synchronize from the same cluster during fail back.

5.8.4. Recover from a disaster with two-way mirroring

To recover from a disaster when using two-way mirroring use the following procedures. They show how to fail over to the mirrored data on the secondary cluster after the primary cluster terminates, and how to failback. The shutdown can be orderly or non-orderly.

Additional Resources

  • For details on demoting, promoting, and resyncing images, see the Configure mirroring on a image section in the Red Hat Ceph Storage Block Device Guide.

5.8.5. Failover after an orderly shutdown

Failover to the secondary storage cluster after an orderly shutdown.

Prerequisites

  • Minimum of two running Red Hat Ceph Storage clusters.
  • Root-level access to the node.
  • Pool mirroring or image mirroring configured with one-way mirroring.

Procedure

  1. Stop all clients that use the primary image. This step depends on which clients use the image. For example, detach volumes from any OpenStack instances that use the image.
  2. Demote the primary images located on the site-a cluster by running the following commands on a monitor node in the site-a cluster:

    Syntax

    rbd mirror image demote POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd mirror image demote data/image1
    [root@rbd-client ~]# rbd mirror image demote data/image2

  3. Promote the non-primary images located on the site-b cluster by running the following commands on a monitor node in the site-b cluster:

    Syntax

    rbd mirror image promote POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd mirror image promote data/image1
    [root@rbd-client ~]# rbd mirror image promote data/image2

  4. After some time, check the status of the images from a monitor node in the site-b cluster. They should show a state of up+stopped and be listed as primary:

    [root@rbd-client ~]# rbd mirror image status data/image1
    image1:
      global_id:   08027096-d267-47f8-b52e-59de1353a034
      state:       up+stopped
      description: local image is primary
      last_update: 2019-04-17 16:04:37
    [root@rbd-client ~]# rbd mirror image status data/image2
    image2:
      global_id:   596f41bc-874b-4cd4-aefe-4929578cc834
      state:       up+stopped
      description: local image is primary
      last_update: 2019-04-17 16:04:37
  5. Resume the access to the images. This step depends on which clients use the image.

Additional Resources

5.8.6. Failover after a non-orderly shutdown

Failover to secondary storage cluster after a non-orderly shutdown.

Prerequisites

  • Minimum of two running Red Hat Ceph Storage clusters.
  • Root-level access to the node.
  • Pool mirroring or image mirroring configured with one-way mirroring.

Procedure

  1. Verify that the primary storage cluster is down.
  2. Stop all clients that use the primary image. This step depends on which clients use the image. For example, detach volumes from any OpenStack instances that use the image.
  3. Promote the non-primary images from a Ceph Monitor node in the site-b storage cluster. Use the --force option, because the demotion cannot be propagated to the site-a storage cluster:

    Syntax

    rbd mirror image promote --force POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd mirror image promote --force data/image1
    [root@rbd-client ~]# rbd mirror image promote --force data/image2

  4. Check the status of the images from a Ceph Monitor node in the site-b storage cluster. They should show a state of up+stopping_replay and the description should say force promoted:

    Example

    [root@rbd-client ~]# rbd mirror image status data/image1
    image1:
      global_id:   08027096-d267-47f8-b52e-59de1353a034
      state:       up+stopping_replay
      description: force promoted
      last_update: 2019-04-17 13:25:06
    [root@rbd-client ~]# rbd mirror image status data/image2
    image2:
      global_id:   596f41bc-874b-4cd4-aefe-4929578cc834
      state:       up+stopping_replay
      description: force promoted
      last_update: 2019-04-17 13:25:06

Additional Resources

5.8.7. Prepare for fail back

If two storage clusters were originally configured only for one-way mirroring, in order to fail back, configure the primary storage cluster for mirroring in order to replicate the images in the opposite direction.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. On the client node of the site-a storage cluster, install the rbd-mirror package:

    [root@rbd-client ~]# yum install rbd-mirror
    Note

    The package is provided by the Red Hat Ceph Storage Tools repository.

  2. On the client node of the site-a storage cluster, specify the storage cluster name by adding the CLUSTER option to the /etc/sysconfig/ceph file:

    CLUSTER=site-b
  3. Copy the site-b Ceph configuration file and keyring file from the site-b Ceph Monitor node to the site-a Ceph Monitor and client nodes:

    Syntax

    scp /etc/ceph/ceph.conf USER@SITE_A_MON_NODE_NAME:/etc/ceph/site-b.conf
    scp /etc/ceph/site-b.client.site-b.keyring root@SITE_A_MON_NODE_NAME:/etc/ceph/
    scp /etc/ceph/ceph.conf user@SITE_A_CLIENT_NODE_NAME:/etc/ceph/site-b.conf
    scp /etc/ceph/site-b.client.site-b.keyring user@SITE_A_CLIENT_NODE_NAME:/etc/ceph/

    Note

    The scp commands that transfer the Ceph configuration file from the site-b Ceph Monitor node to the site-a Ceph Monitor and client nodes renames the file to site-a.conf. The keyring file name stays the same.

  4. Copy the site-a keyring file from the site-a Ceph Monitor node to the site-a client node:

    Syntax

    scp /etc/ceph/site-a.client.site-a.keyring <user>@SITE_A_CLIENT_HOST_NAME:/etc/ceph/

  5. Enable and start the rbd-mirror daemon on the site-a client node:

    Syntax

    systemctl enable ceph-rbd-mirror.target
    systemctl enable ceph-rbd-mirror@CLIENT_ID
    systemctl start ceph-rbd-mirror@CLIENT_ID

    Change CLIENT_ID to the Ceph Storage cluster user that the rbd-mirror daemon will use. The user must have the appropriate cephx access to the storage cluster.

    Example

    [root@rbd-client ~]# systemctl enable ceph-rbd-mirror.target
    [root@rbd-client ~]# systemctl enable ceph-rbd-mirror@site-a
    [root@rbd-client ~]# systemctl start ceph-rbd-mirror@site-a

  6. From the client node on the site-a cluster, add the site-b cluster as a peer:

    Example

    [root@rbd-client ~]# rbd --cluster site-a mirror pool peer add data client.site-b@site-b -n client.site-a

    If you are using multiple secondary storage clusters, only the secondary storage cluster chosen to fail over to, and fail back from, must be added.

  7. From a monitor node in the site-a storage cluster, verify the site-b storage cluster was successfully added as a peer:

    Example

    [root@rbd-client ~]# rbd mirror pool info -p data
    Mode: image
    Peers:
      UUID                                 NAME   CLIENT
      d2ae0594-a43b-4c67-a167-a36c646e8643 site-b client.site-b

Additional Resources

  • For detailed information, see the User Management chapter in the Red Hat Ceph Storage Administration Guide.

5.8.7.1. Fail back to the primary storage cluster

When the formerly primary storage cluster recovers, fail back to the primary storage cluster.

Prerequisites

  • Minimum of two running Red Hat Ceph Storage clusters.
  • Root-level access to the node.
  • Pool mirroring or image mirroring configured with one-way mirroring.

Procedure

  1. Check the status of the images from a monitor node in the site-b cluster again. They should show a state of up-stopped and the description should say local image is primary:

    Example

    [root@rbd-client ~]# rbd mirror image status data/image1
    image1:
      global_id:   08027096-d267-47f8-b52e-59de1353a034
      state:       up+stopped
      description: local image is primary
      last_update: 2019-04-22 17:37:48
    [root@rbd-client ~]# rbd mirror image status data/image2
    image2:
      global_id:   08027096-d267-47f8-b52e-59de1353a034
      state:       up+stopped
      description: local image is primary
      last_update: 2019-04-22 17:38:18

  2. From a Ceph Monitor node on the site-a storage cluster determine if the images are still primary:

    Syntax

    rbd mirror pool info POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd info data/image1
    [root@rbd-client ~]# rbd info data/image2

    In the output from the commands, look for mirroring primary: true or mirroring primary: false, to determine the state.

  3. Demote any images that are listed as primary by running a command like the following from a Ceph Monitor node in the site-a storage cluster:

    Syntax

    rbd mirror image demote POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd mirror image demote data/image1

  4. Resynchronize the images ONLY if there was a non-orderly shutdown. Run the following commands on a monitor node in the site-a storage cluster to resynchronize the images from site-b to site-a:

    Syntax

    rbd mirror image resync POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd mirror image resync data/image1
    Flagged image for resync from primary
    [root@rbd-client ~]# rbd mirror image resync data/image2
    Flagged image for resync from primary

  5. After some time, ensure resynchronization of the images is complete by verifying they are in the up+replaying state. Check their state by running the following commands on a monitor node in the site-a storage cluster:

    Syntax

    rbd mirror image status POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd mirror image status data/image1
    [root@rbd-client ~]# rbd mirror image status data/image2

  6. Demote the images on the site-b storage cluster by running the following commands on a Ceph Monitor node in the site-b storage cluster:

    Syntax

    rbd mirror image demote POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd mirror image demote data/image1
    [root@rbd-client ~]# rbd mirror image demote data/image2

    Note

    If there are multiple secondary storage clusters, this only needs to be done from the secondary storage cluster where it was promoted.

  7. Promote the formerly primary images located on the site-a storage cluster by running the following commands on a Ceph Monitor node in the site-a storage cluster:

    Syntax

    rbd mirror image promote POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd mirror image promote data/image1
    [root@rbd-client ~]# rbd mirror image promote data/image2

  8. Check the status of the images from a Ceph Monitor node in the site-a storage cluster. They should show a status of up+stopped and the description should say local image is primary:

    Syntax

    rbd mirror image status POOL_NAME/IMAGE_NAME

    Example

    [root@rbd-client ~]# rbd mirror image status data/image1
    image1:
      global_id:   08027096-d267-47f8-b52e-59de1353a034
      state:       up+stopped
      description: local image is primary
      last_update: 2019-04-22 11:14:51
    [root@rbd-client ~]# rbd mirror image status data/image2
    image2:
      global_id:   596f41bc-874b-4cd4-aefe-4929578cc834
      state:       up+stopped
      description: local image is primary
      last_update: 2019-04-22 11:14:51

5.8.8. Remove two-way mirroring

After fail back is complete, you can remove two-way mirroring and disable the Ceph block device mirroring service.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. Remove the site-b storage cluster as a peer from the site-a storage cluster:

    Example

    [root@rbd-client ~]# rbd mirror pool peer remove data client.remote@remote --cluster local
    [root@rbd-client ~]# rbd --cluster site-a mirror pool peer remove data client.site-b@site-b -n client.site-a

  2. Stop and disable the rbd-mirror daemon on the site-a client:

    Syntax

    systemctl stop ceph-rbd-mirror@CLIENT_ID
    systemctl disable ceph-rbd-mirror@CLIENT_ID
    systemctl disable ceph-rbd-mirror.target

    Example

    [root@rbd-client ~]# systemctl stop ceph-rbd-mirror@site-a
    [root@rbd-client ~]# systemctl disable ceph-rbd-mirror@site-a
    [root@rbd-client ~]# systemctl disable ceph-rbd-mirror.target

Chapter 6. Using the Ceph block device Python module

The rbd python module provides file-like access to Ceph block device images. In order to use this built-in tool, import the rbd and rados Python modules.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to the node.

Procedure

  1. Connect to RADOS and open an IO context:

    cluster = rados.Rados(conffile='my_ceph.conf')
    cluster.connect()
    ioctx = cluster.open_ioctx('mypool')
  2. Instantiate an :class:rbd.RBD object, which you use to create the image:

    rbd_inst = rbd.RBD()
    size = 4 * 1024**3  # 4 GiB
    rbd_inst.create(ioctx, 'myimage', size)
  3. To perform I/O on the image, instantiate an :class:rbd.Image object:

    image = rbd.Image(ioctx, 'myimage')
    data = 'foo' * 200
    image.write(data, 0)

    This writes 'foo' to the first 600 bytes of the image. Note that data cannot be :type:unicode - librbd does not know how to deal with characters wider than a :c:type:char.

  4. Close the image, the IO context and the connection to RADOS:

    image.close()
    ioctx.close()
    cluster.shutdown()

    To be safe, each of these calls must to be in a separate :finally block:

    import rados
    import rbd
    
    cluster = rados.Rados(conffile='my_ceph_conf')
    try:
        ioctx = cluster.open_ioctx('my_pool')
        try:
            rbd_inst = rbd.RBD()
            size = 4 * 1024**3  # 4 GiB
            rbd_inst.create(ioctx, 'myimage', size)
            image = rbd.Image(ioctx, 'myimage')
            try:
                data = 'foo' * 200
                image.write(data, 0)
            finally:
                image.close()
        finally:
            ioctx.close()
    finally:
        cluster.shutdown()

    This can be cumbersome, so the Rados, Ioctx, and Image classes can be used as context managers that close or shut down automatically. Using them as context managers, the above example becomes:

    with rados.Rados(conffile='my_ceph.conf') as cluster:
        with cluster.open_ioctx('mypool') as ioctx:
            rbd_inst = rbd.RBD()
            size = 4 * 1024**3  # 4 GiB
            rbd_inst.create(ioctx, 'myimage', size)
            with rbd.Image(ioctx, 'myimage') as image:
                data = 'foo' * 200
                image.write(data, 0)

Chapter 7. The Ceph iSCSI Gateway

As a storage administrator, you can install and configure an iSCSI gateway for the Red Hat Ceph Storage cluster. With Ceph’s iSCSI gateway you can effectively run a fully integrated block-storage infrastructure with all features and benefits of a conventional Storage Area Network (SAN).

7.1. Introduction to the Ceph iSCSI gateway

Traditionally, block-level access to a Ceph storage cluster has been limited to QEMU and librbd, which is a key enabler for adoption within OpenStack environments. Block-level access to the Ceph storage cluster can now take advantage of the iSCSI standard to provide data storage.

The iSCSI gateway integrates Red Hat Ceph Storage with the iSCSI standard to provide a highly available (HA) iSCSI target that exports RADOS Block Device (RBD) images as SCSI disks. The iSCSI protocol allows clients, known as initiators, to send SCSI commands to SCSI storage devices, known as targets, over a TCP/IP network. This allows for heterogeneous clients, such as Microsoft Windows, to access the Red Hat Ceph Storage cluster.

Figure 7.1. Ceph iSCSI Gateway HA Design

Ceph iSCSI HA 424879 1116 ECE 01

7.2. Requirements for the iSCSI target

The Red Hat Ceph Storage Highly Available (HA) iSCSI gateway solution has requirements for the number of gateway nodes, memory capacity, and timer settings to detect down OSDs.

Required Number of Nodes

Install a minimum of two iSCSI gateway nodes. To increase resiliency and I/O handling, install up to four iSCSI gateway nodes.

Memory Requirements

The memory footprint of the RBD images can grow to a large size. Each RBD image mapped on the iSCSI gateway nodes uses roughly 90 MB of memory. Ensure the iSCSI gateway nodes have enough memory to support each mapped RBD image.

Detecting Down OSDs

There are no specific iSCSI gateway options for the Ceph Monitors or OSDs, but it is important to lower the default timers for detecting down OSDs to reduce the possibility of initiator timeouts. Follow the instructions in Lowering timer settings for detecting down OSDs to reduce the possibility of initiator timeouts.

Additional Resources

7.3. Installing the iSCSI gateway

As a storage administrator, before you can utilize the benefits of the Ceph iSCSI gateway, you must install the required software packages. You can install the Ceph iSCSI gateway by using the Ansible deployment tool, or by using the command-line interface.

Each iSCSI gateway runs the Linux I/O target kernel subsystem (LIO) to provide iSCSI protocol support. LIO utilizes a user-space passthrough (TCMU) to interact with the Ceph librbd library to expose RBD images to iSCSI clients. With the Ceph iSCSI gateway you can effectively run a fully integrated block-storage infrastructure with all features and benefits of a conventional Storage Area Network (SAN).

7.3.1. Prerequisites

  • Red Hat Enterprise Linux 8 or 7.7 or higher.
  • A running Red Hat Ceph Storage 4 or higher cluster.

7.3.2. Installing the Ceph iSCSI gateway using Ansible

Use the Ansible utility to install packages and set up the daemons for the Ceph iSCSI gateway.

Prerequisites

  • The Ansible administration node with the ceph-ansible package installed.

Procedure

  1. On the iSCSI gateway nodes, enable the Red Hat Ceph Storage 4 Tools repository. For details, see the Enabling the Red Hat Ceph Storage Repositories section in the Red Hat Ceph Storage Installation Guide.
  2. On the Ansible administration node, add an entry in /etc/ansible/hosts file for the gateway group. If you colocate the iSCSI gateway with an OSD node, add the OSD node to the [iscsigws] section.

    [iscsigws]
    ceph-igw-1
    ceph-igw-2
  3. Ansible places a file in the /usr/share/ceph-ansible/group_vars/ directory called iscsigws.yml.sample. Create a copy of the iscsigws.yml.sample file named it iscsigws.yml.
  4. Optionally, review the Ansible variables and descriptions in the iSCSI Gateway Variables section and update iscsigws.yml as needed.

    Warning

    Gateway configuration changes are only supported from one gateway at a time. Attempting to run changes concurrently through multiple gateways might lead to configuration instability and inconsistency.

    Warning

    Ansible installs the ceph-iscsi package, creates, and updates the /etc/ceph/iscsi-gateway.cfg file based on settings in the group_vars/iscsigws.yml file when the ansible-playbook command is used. If you have previously installed the ceph-iscsi package using the command-line interface described in Installing the iSCSI gateway using the command-line interface, copy the existing settings from the iscsi-gateway.cfg file to the group_vars/iscsigws.yml file.

  5. On the Ansible administration node, execute the Ansible playbook.

    • Bare-metal deployments:

      [admin@ansible ~]$ cd /usr/share/ceph-ansible
      [admin@ansible ceph-ansible]$ ansible-playbook site.yml -i hosts
    • Container deployments:

      [admin@ansible ~]$ cd /usr/share/ceph-ansible
      [admin@ansible ceph-ansible]$ ansible-playbook site-container.yml -i hosts
      Warning

      On stand-alone iSCSI gateway nodes, verify that the correct Red Hat Ceph Storage 4 software repositories are enabled. If they are unavailable, Ansible might install incorrect packages.

  6. To create targets, LUNs, and clients, use the gwcli utility or the Red Hat Ceph Storage Dashboard.

    Important

    Do not use the targetcli utility to change the configuration, this will result in the following issues: ALUA misconfiguration and path failover problems. There is the potential to corrupt data, to have mismatched configuration across iSCSI gateways, and to have mismatched WWN information, which will lead to client pathing problems.

7.3.3. Installing the Ceph iSCSI gateway using the command-line interface

The Ceph iSCSI gateway is the iSCSI target node and also a Ceph client node. The Ceph iSCSI gateway can be a standalone node or be colocated on a Ceph Object Store Disk (OSD) node. Complete the following steps to install the Ceph iSCSI gateway.

Prerequisites

  • Red Hat Enterprise Linux 8 or 7.7 and later
  • A Red Hat Ceph Storage 4 cluster or later
  • On all Ceph Monitor nodes in the storage cluster, restart the ceph-mon service, as the root user:

    Syntax

    systemctl restart ceph-mon@MONITOR_HOST_NAME

    Example

    [root@mon ~]# systemctl restart ceph-mon@monitor1

  • If the Ceph iSCSI gateway is not colocated on an OSD node, copy the Ceph configuration files, located in the /etc/ceph/ directory, from a running Ceph node in the storage cluster to the all iSCSI Gateway nodes. The Ceph configuration files must exist on the iSCSI gateway nodes under /etc/ceph/.
  • On all Ceph iSCSI gateway nodes, enable the Ceph Tools repository. For details see the Enabling the Red Hat Ceph Storage Repositories section in the Installation Guide.
  • On all Ceph iSCSI gateway nodes, install and configure the Ceph command-line interface. For details, see the Installing the Ceph Command Line Interface chapter in the Red Hat Ceph Storage 4 Installation Guide.
  • If needed, open TCP ports 3260 and 5000 on the firewall on all Ceph iSCSI nodes.
  • Create a new or use an existing RADOS Block Device (RBD).

Procedure

  1. On all Ceph iSCSI gateway nodes, install the ceph-iscsi and tcmu-runner packages:

    [root@iscsigw ~]# yum install ceph-iscsi tcmu-runner
    Important

    If previous versions of these packages exist, remove them before installing the newer versions. You must install these newer versions from a Red Hat Ceph Storage repository.

  2. Optionally, on all Ceph iSCSI gateway nodes, install and configure the OpenSSL utility, if needed.

    1. Install the openssl package:

      [root@iscsigw ~]# yum install openssl
    2. On the primary iSCSI gateway node, create a directory to hold the SSL keys:

      [root@iscsigw ~]# mkdir ~/ssl-keys
      [root@iscsigw ~]# cd ~/ssl-keys
    3. On the primary iSCSI gateway node, create the certificate and key files. Enter the environmental information when prompted.

      [root@iscsigw ~]# openssl req -newkey rsa:2048 -nodes -keyout iscsi-gateway.key -x509 -days 365 -out iscsi-gateway.crt
    4. On the primary iSCSI gateway node, create a PEM file:

      [root@iscsigw ~]# cat iscsi-gateway.crt iscsi-gateway.key > iscsi-gateway.pem
    5. On the primary iSCSI gateway node, create a public key:

      [root@iscsigw ~]# openssl x509 -inform pem -in iscsi-gateway.pem -pubkey -noout > iscsi-gateway-pub.key
    6. From the primary iSCSI gateway node, copy the iscsi-gateway.crt, iscsi-gateway.pem, iscsi-gateway-pub.key, and iscsi-gateway.key files to the /etc/ceph/ directory on the other iSCSI gateway nodes.
  3. Create a configuration file on a Ceph iSCSI gateway node, and then copy it to all iSCSI gateway nodes.

    1. Create a file named iscsi-gateway.cfg in the /etc/ceph/ directory:

      [root@iscsigw ~]# touch /etc/ceph/iscsi-gateway.cfg
    2. Edit the iscsi-gateway.cfg file and add the following lines:

      Syntax

      [config]
      cluster_name = CLUSTER_NAME
      gateway_keyring = CLIENT_KEYRING
      api_secure = false
      trusted_ip_list = IP_ADDR,IP_ADDR

      Example

      [config]
      cluster_name = ceph
      gateway_keyring = ceph.client.admin.keyring
      api_secure = false
      trusted_ip_list = 192.168.0.10,192.168.0.11

    3. Copy the iscsi-gateway.cfg file to all iSCSI gateway nodes. Note that the file must be identical on all iSCSI gateway nodes.
  4. On all Ceph iSCSI gateway nodes, enable and start the API services:

    [root@iscsigw ~]# systemctl enable rbd-target-api
    [root@iscsigw ~]# systemctl start rbd-target-api
    [root@iscsigw ~]# systemctl enable rbd-target-gw
    [root@iscsigw ~]# systemctl start rbd-target-gw
  5. Next, configure targets, LUNs, and clients. See the Configuring the iSCSI target using the command-line interface section for details.

Additional Resources

7.3.4. Additional Resources

7.4. Configuring the iSCSI target

As a storage administrator, you can configure targets, LUNs, and clients, using the gwcli command-line utility. You can also optimize performance of the iSCSI target, use the gwcli reconfigure subcommand.

Warning

Red Hat does not support managing Ceph block device images exported by the Ceph iSCSI gateway tools, such as gwcli and ceph-ansible. Also, using the rbd command to rename or remove RBD images exported by the Ceph iSCSI gateway, can result in an unstable storage cluster.

Warning

Before removing RBD images from the iSCSI gateway configuration, follow the standard procedures for removing a storage device from the operating system. For details, see the Removing a storage device chapter in the Storage Administration Guide for Red Hat Enterprise Linux 7 or the System Design Guide for Red Hat Enterprise Linux 8.

7.4.1. Prerequisites

  • Installation of the Ceph iSCSI gateway software.

7.4.2. Configuring the iSCSI target using the command-line interface

The Ceph iSCSI gateway is the iSCSI target node and also a Ceph client node. Configure the Ceph iSCSI gateway either on a standalone node, or colocate it with a Ceph Object Storage Device (OSD) node.

Warning

Do not adjust other options using the gwcli reconfigure subcommand unless specified in this document or Red Hat Support has instructed you to do so.

Prerequisites

  • Installation of the Ceph iSCSI gateway software.

Procedure

  1. Start the iSCSI gateway command-line interface:

    [root@iscsigw ~]# gwcli
  2. Create the iSCSI gateways using either IPv4 or IPv6 addresses:

    Syntax

    >/iscsi-targets create iqn.2003-01.com.redhat.iscsi-gw:_target_name_
    > goto gateways
    > create ISCSI_GW_NAME IP_ADDR_OF_GW
    > create ISCSI_GW_NAME IP_ADDR_OF_GW

    Example

    >/iscsi-targets create iqn.2003-01.com.redhat.iscsi-gw:ceph-igw
    > goto gateways
    > create ceph-gw-1 10.172.19.21
    > create ceph-gw-2 10.172.19.22

    Note

    You cannot use a mix of IPv4 and IPv6 addresses.

  3. Add a Ceph block device:

    Syntax

    > cd /disks
    >/disks/ create POOL_NAME image=IMAGE_NAME size=IMAGE_SIZE_m|g|t

    Example

    > cd /disks
    >/disks/ create rbd image=disk_1 size=50g

    Note

    Do not use any periods (.) in the pool or image name.

  4. Create a client:

    Syntax

    > goto hosts
    > create iqn.1994-05.com.redhat:_client_name_
    > auth use username=USER_NAME password=PASSWORD

    Example

    > goto hosts
    > create iqn.1994-05.com.redhat:rh7-client
    > auth username=iscsiuser1 password=temp12345678

    Important

    Red Hat does not support mixing clients, some with Challenge Handshake Authentication Protocol (CHAP) enabled and some CHAP disabled. All clients must have either CHAP enabled or have CHAP disabled. The default behavior is to only authenticate an initiator by its initiator name.

    If initiators are failing to log into the target, the CHAP authentication might not be configured correctly for some initiators, for example:

    o- hosts ................................ [Hosts: 2: Auth: MISCONFIG]

    Use the following command at the hosts level to reset all the CHAP authentication:

    /> goto hosts
    /iscsi-target...csi-igw/hosts> auth nochap
    ok
    ok
    /iscsi-target...csi-igw/hosts> ls
    o- hosts ................................ [Hosts: 2: Auth: None]
      o- iqn.2005-03.com.ceph:esx ........... [Auth: None, Disks: 4(310G)]
      o- iqn.1994-05.com.redhat:rh7-client .. [Auth: None, Disks: 0(0.00Y)]
  5. Add disks to a client:

    Syntax

    >/iscsi-target..eph-igw/hosts
    > cd iqn.1994-05.com.redhat:_CLIENT_NAME_
    > disk add POOL_NAME/IMAGE_NAME

    Example

    >/iscsi-target..eph-igw/hosts
    > cd iqn.1994-05.com.redhat:rh7-client
    > disk add rbd/disk_1

  6. To confirm that the API is using SSL correctly, search the rbd-target-api log file, located at /var/log/rbd-target-api.log or /var/log/rbd-target/rbd-target-api.log, for https, for example:

    Aug 01 17:27:42 test-node.example.com python[1879]:  * Running on https://0.0.0.0:5000/
  7. Verifying that the Ceph ISCSI gateways are working:

    /> goto gateways
    /iscsi-target...-igw/gateways> ls
    o- gateways ............................ [Up: 2/2, Portals: 2]
      o- ceph-gw-1  ........................ [ 10.172.19.21 (UP)]
      o- ceph-gw-2  ........................ [ 10.172.19.22 (UP)]

    If the status is UNKNOWN, check for network issues and any misconfigurations. If using a firewall, verify that the appropriate TCP port is open. Verify that the iSCSI gateway is listed in the trusted_ip_list option. Verify that the rbd-target-api service is running on the iSCSI gateway node.

  8. Optionally, reconfigure the max_data_area_mb option:

    Syntax

    >/disks/ reconfigure POOL_NAME/IMAGE_NAME max_data_area_mb NEW_BUFFER_SIZE

    Example

    >/disks/ reconfigure rbd/disk_1 max_data_area_mb 64

    Note

    The max_data_area_mb option controls the amount of memory in megabytes that each image can use to pass SCSI command data between the iSCSI target and the Ceph cluster. If this value is too small, it can result in excessive queue full retries which will affect performance. If the value is too large, it can result in one disk using too much of the system memory, which can cause allocation failures for other subsystems. The default value for the max_data_area_mb option is 8.

  9. Configure an iSCSI initiator.

Additional Resources

7.4.3. Optimize the performance of the iSCSI Target

There are many settings that control how the iSCSI Target transfers data over the network. These settings can be used to optimize the performance of the iSCSI gateway.

Warning

Only change these settings if instructed to by Red Hat Support or as specified in this document.

The gwcli reconfigure subcommand controls the settings that are used to optimize the performance of the iSCSI gateway.

Settings that affect the performance of the iSCSI target

  • max_data_area_mb
  • cmdsn_depth
  • immediate_data
  • initial_r2t
  • max_outstanding_r2t
  • first_burst_length
  • max_burst_length
  • max_recv_data_segment_length
  • max_xmit_data_segment_length

Additional Resources

7.4.4. Lowering timer settings for detecting down OSDs

Sometimes it is necessary to lower the timer settings for detecting down OSDs. For example, when using Red Hat Ceph Storage as an iSCSI gateway, you can reduce the possibility of initiator timeouts by lowering the timer settings for detecting down OSDs.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Access to the Ansible administration node.

Procedure

  1. Configure Ansible to use the new timer settings.

    1. On the Ansible administration node, add a ceph_conf_overrides section in the group_vars/all.yml file that looks like this, or edit any existing ceph_conf_overrides section as follows:

      ceph_conf_overrides:
           osd:
             osd_client_watch_timeout: 15
             osd_heartbeat_grace: 20
             osd_heartbeat_interval: 5

      The above settings will be added to the ceph.conf configuration files on the OSD nodes when the Ansible playbook runs.

    2. Change to the ceph-ansible directory:

      [admin@ansible ~]$ cd /usr/share/ceph-ansible
    3. Use Ansible to update the ceph.conf file and restart the OSD daemons on all the OSD nodes. On the Ansible admin node, run the following command:

      Bare-metal Deployments

      [admin@ansible ceph-ansible]$ ansible-playbook site.yml --limit osds

      Container Deployments

      [admin@ansible ceph-ansible]$ ansible-playbook site-container.yml --limit osds -i hosts

  2. Verify the timer settings are the same as set in ceph_conf_overrides:

    Syntax

    ceph daemon osd.OSD_ID config get osd_client_watch_timeout
    ceph daemon osd.OSD_ID config get osd_heartbeat_grace
    ceph daemon osd.OSD_ID config get osd_heartbeat_interval

    Example

    [root@osd ~]# ceph daemon osd.0 config get osd_client_watch_timeout
    {
        "osd_client_watch_timeout": "15"
    }
    
    [root@osd ~]#  ceph daemon osd.0 config get osd_heartbeat_grace
    {
        "osd_heartbeat_grace": "20"
    }
    
    [root@osd ~]# ceph daemon osd.0 config get osd_heartbeat_interval
    {
        "osd_heartbeat_interval": "5"
    }

  3. Optional: If you cannot restart the OSD daemons immediately, you can do online updates from Ceph Monitor nodes, or update all Ceph OSD nodes directly. Once you are able to restart the OSD daemons, use Ansible as described above to add the new timer settings into ceph.conf so that the settings persist across reboots.

    1. To do an online update of OSD timer settings from a Ceph Monitor node:

      Syntax

      ceph tell osd.OSD_ID injectargs '--osd_client_watch_timeout 15'
      ceph tell osd.OSD_ID injectargs '--osd_heartbeat_grace 20'
      ceph tell osd.OSD_ID injectargs '--osd_heartbeat_interval 5'

      Example

      [root@mon ~]# ceph tell osd.0 injectargs '--osd_client_watch_timeout 15'
      [root@mon ~]# ceph tell osd.0 injectargs '--osd_heartbeat_grace 20'
      [root@mon ~]# ceph tell osd.0 injectargs '--osd_heartbeat_interval 5'

    2. To do an online update of OSD timer settings from an Ceph OSD node:

      Syntax

      ceph daemon osd.OSD_ID config set osd_client_watch_timeout 15
      ceph daemon osd.OSD_ID config set osd_heartbeat_grace 20
      ceph daemon osd.OSD_ID config set osd_heartbeat_interval 5

      Example

      [root@osd ~]# ceph daemon osd.0 config set osd_client_watch_timeout 15
      [root@osd ~]# ceph daemon osd.0 config set osd_heartbeat_grace 20
      [root@osd ~]# ceph daemon osd.0 config set osd_heartbeat_interval 5

Additional Resources

  • For more information about using Red Hat Ceph Storage as an iSCSI gateway, see The Ceph iSCSI gateway in the Red Hat Ceph Storage Block Device Guide.

7.4.5. Configuring iSCSI host groups using the command-line interface

The Ceph iSCSI gateway can configure host groups for managing multiple servers that share the same disk configuration. iSCSI host groups creates a logical grouping of hosts and the disks that each host in the group has access to.

Important

The sharing of disk devices to multiple hosts must use a cluster-aware file system.

Prerequisites

  • Installation of the Ceph iSCSI gateway software.
  • Root-level access to the Ceph iSCSI gateway node.

Procedure

  1. Start the iSCSI gateway command-line interface:

    [root@iscsigw ~]# gwcli
  2. Create a new host group:

    Syntax

    cd iscsi-targets/
    cd IQN/host-groups
    create group_name=GROUP_NAME

    Example

    /> cd iscsi-targets/
    /iscsi-targets> cd iqn.2003-01.com.redhat.iscsi-gw:ceph-igw/host-groups/
    /iscsi-target.../host-groups> create group_name=igw_grp01

  3. Add a host to the host group:

    Syntax

    cd GROUP_NAME
    host add client_iqn=CLIENT_IQN

    Example

    > cd igw_grp01
    /iscsi-target.../host-groups/igw_grp01> host add client_iqn=iqn.1994-05.com.redhat:rh8-client

    Repeat this step to add additional hosts to the group.

  4. Add a disk to the host group:

    Syntax

    cd /disks/
    /disks> create pool=POOL image=IMAGE_NAME size=SIZE
    cd /IQN/host-groups/GROUP_NAME
    disk add POOL/IMAGE_NAME

    Example

    > cd /disks/
    /disks> create pool=rbd image=rbdimage size=1G
    /> cd iscsi-targets/iqn.2003-01.com.redhat.iscsi-gw:ceph-igw/host-groups/igw_grp01/
    /iscsi-target...s/igw_grp01> disk add rbd/rbdimage

    Repeat this step to add additional disks to the group.

7.4.6. Additional Resources

  • For details on configuring iSCSI targets using the Red Hat Ceph Storage Dashboard, see the Creating iSCSI targets section in the Red Hat Ceph Storage Dashboard Guide.

7.5. Configuring the iSCSI initiator

You can configure the iSCSI initiator to connect to the Ceph iSCSI gateway on the following platforms.

7.5.1. Configuring the iSCSI initiator for Red Hat Enterprise Linux

Prerequisites

  • Red Hat Enterprise Linux 7.7 or higher.
  • Package iscsi-initiator-utils-6.2.0.873-35 or newer must be installed.
  • Package device-mapper-multipath-0.4.9-99 or newer must be installed.

Procedure

  1. Install the iSCSI initiator and multipath tools:

    [root@rhel ~]# yum install iscsi-initiator-utils
    [root@rhel ~]# yum install device-mapper-multipath
  2. Set the initiator name by editing the /etc/iscsi/initiatorname.iscsi file. Note that the initiator name must match the initiator name that was used during the initial setup using the gwcli command.
  3. Configure multipath I/O.

    1. Create the default /etc/multipath.conf file and enable the multipathd service:

      [root@rhel ~]# mpathconf --enable --with_multipathd y
    2. Update the /etc/multipath.conf file as follows:

      devices {
              device {
                      vendor                 "LIO-ORG"
                      product                "TCMU device"
                      hardware_handler       "1 alua"
                      path_grouping_policy   "failover"
                      path_selector          "queue-length 0"
                      failback               60
                      path_checker           tur
                      prio                   alua
                      prio_args              exclusive_pref_bit
                      fast_io_fail_tmo       25
                      no_path_retry          queue
              }
      }
    3. Restart the multipathd service:

      [root@rhel ~]# systemctl reload multipathd
  4. Set up CHAP and iSCSI discovery and login.

    1. Provide a CHAP user name and password by updating the /etc/iscsi/iscsid.conf file accordingly, for example:

      node.session.auth.authmethod = CHAP
      node.session.auth.username = user
      node.session.auth.password = password
    2. Discover the target portals:

      Syntax

      iscsiadm -m discovery -t st -p IP_ADDR

    3. Log in to target:

      Syntax

      iscsiadm -m node -T TARGET -l

  5. View the multipath I/O configuration. The multipathd daemon sets up devices automatically based on the settings in the multipath.conf file.

    1. Use the multipath command to show devices setup in a failover configuration with a priority group for each path, for example:

      Example

      [root@rhel ~]# multipath -ll
      mpathbt (360014059ca317516a69465c883a29603) dm-1 LIO-ORG,TCMU device
      size=1.0G features='0' hwhandler='1 alua' wp=rw
      |-+- policy='queue-length 0' prio=50 status=active
      | `- 28:0:0:1 sde  8:64  active ready running
      `-+- policy='queue-length 0' prio=10 status=enabled
        `- 29:0:0:1 sdc  8:32  active ready running

      The multipath -ll output prio value indicates the ALUA state, where prio=50 indicates it is the path to the owning iSCSI gateway in the ALUA Active-Optimized state and prio=10 indicates it is an Active-non-Optimized path. The status field indicates which path is being used, where active indicates the currently used path, and enabled indicates the failover path, if the active fails.

    2. To match the device name, for example, sde in the multipath -ll output, to the iSCSI gateway:

      Example

      [root@rhel ~]# iscsiadm -m session -P 3

      The Persistent Portal value is the IP address assigned to the iSCSI gateway listed in the gwcli utility.

7.5.2. Configuring the iSCSI initiator for Red Hat Virtualization

Prerequisites

  • Red Hat Virtualization 4.1
  • Configured MPIO devices on all Red Hat Virtualization nodes
  • The iscsi-initiator-utils-6.2.0.873-35 package or newer
  • The device-mapper-multipath-0.4.9-99 package or newer

Procedure

  1. Configure multipath I/O.

    1. Create the default /etc/multipath.conf file and enable the multipathd service:

      [root@rhv ~]# mpathconf --enable --with_multipathd y
    2. Update the /etc/multipath.conf file as follows:

      devices {
              device {
                      vendor                 "LIO-ORG"
                      product                "TCMU device"
                      hardware_handler       "1 alua"
                      path_grouping_policy   "failover"
                      path_selector          "queue-length 0"
                      failback               60
                      path_checker           tur
                      prio                   alua
                      prio_args              exclusive_pref_bit
                      fast_io_fail_tmo       25
                      no_path_retry          queue
              }
      }
    3. Restart the multipathd service:

      [root@rhv ~]# systemctl reload multipathd
  2. Click the Storage resource tab to list the existing storage domains.
  3. Click the New Domain button to open the New Domain window.
  4. Enter the Name of the new storage domain.
  5. Use the Data Center drop-down menu to select an data center.
  6. Use the drop-down menus to select the Domain Function and the Storage Type. The storage domain types that are not compatible with the chosen domain function are not available.
  7. Select an active host in the Use Host field. If this is not the first data domain in a data center, you must select the data center’s SPM host.
  8. The New Domain window automatically displays known targets with unused LUNs when iSCSI is selected as the storage type. If the target that you are adding storage from is not listed then you can use target discovery to find it, otherwise proceed to the next step.

    1. Click Discover Targets to enable target discovery options. When targets have been discovered and logged in to, the New Domain window automatically displays targets with LUNs unused by the environment. Note that LUNs external to the environment are also displayed. You can use the Discover Targets options to add LUNs on many targets, or multiple paths to the same LUNs.
    2. Enter the fully qualified domain name or IP address of the iSCSI host in the Address field.
    3. Enter the port to connect to the host on when browsing for targets in the Port field. The default is 3260.
    4. If the Challenge Handshake Authentication Protocol (CHAP) is being used to secure the storage, select the User Authentication check box. Enter the CHAP user name and CHAP password.
    5. Click the Discover button.
    6. Select the target to use from the discovery results and click the Login button. Alternatively, click the Login All to log in to all of the discovered targets.

      Important

      If more than one path access is required, ensure to discover and log in to the target through all the required paths. Modifying a storage domain to add additional paths is currently not supported.

  9. Click the + button next to the desired target. This will expand the entry and display all unused LUNs attached to the target.
  10. Select the check box for each LUN that you are using to create the storage domain.
  11. Optionally, you can configure the advanced parameters.

    1. Click Advanced Parameters.
    2. Enter a percentage value into the Warning Low Space Indicator field. If the free space available on the storage domain is below this percentage, warning messages are displayed to the user and logged.
    3. Enter a GB value into the Critical Space Action Blocker field. If the free space available on the storage domain is below this value, error messages are displayed to the user and logged, and any new action that consumes space, even temporarily, will be blocked.
    4. Select the Wipe After Delete check box to enable the wipe after delete option. You can edit this option after creating the domain, but doing so does not change the wipe after delete property of disks that already exist.
    5. Select the Discard After Delete check box to enable the discard after delete option. You can edit this option after creating the domain. This option is only available to block storage domains.
  12. Click OK to create the storage domain and close the window.

7.5.3. Configuring the iSCSI initiator for Microsoft Windows

Prerequisites

  • Microsoft Windows Server 2016

Procedure

  1. Install the iSCSI initiator and configure discovery and setup.

    1. Install the iSCSI initiator driver and MPIO tools.
    2. Launch the MPIO program, click the Discover Multi-Paths tab, check the Add support for iSCSI devices box, and click Add.
    3. Reboot the MPIO program.
    4. On the iSCSI Initiator Properties window, on the Discovery tab 1 , add a target portal. Enter the IP address or DNS name 2 and Port 3 of the Ceph iSCSI gateway:

      iscsi discovery tab mod
    5. On the Targets tab 1 , select the target and click Connect 2 :

      iscsi target tab mod
    6. On the Connect To Target window, select the Enable multi-path option 1 , and click the Advanced button 2 :

      iscsi connect to target mod
    7. Under the Connect using section, select a Target portal IP 1 . Select Enable CHAP login on 2 and enter the Name and Target secret values 3 from the Ceph iSCSI client credentials section, and click OK 4 :

      iscsi advanced window mod
      Important

      Windows Server 2016 does not accept a CHAP secret less than 12 bytes.

    8. Repeat the previous two steps for each target portal defined when setting up the iSCSI gateway.
    9. If the initiator name is different than the initiator name used during the initial setup, rename the initiator name. From iSCSI Initiator Properties window, on the Configuration tab 1 , click the Change button 2 to rename the initiator name.

      iscsi windows initiator properties mod
  2. Set up multipath I/O. In PowerShell, use the PDORemovePeriod command to set the MPIO load balancing policy and the mpclaim command to set the load balancing policy. The iSCSI Initiator Tool configures the remaining options.

    Note

    Red Hat recommends increasing the PDORemovePeriod option to 120 seconds from PowerShell. You might need to adjust this value based on the application. When all paths are down, and 120 seconds expires, the operating system starts failing I/O requests.

    Set-MPIOSetting -NewPDORemovePeriod 120
    1. Set the failover policy

      mpclaim.exe -l -m 1
    2. Verify the failover policy

      mpclaim -s -m
      MSDSM-wide Load Balance Policy: Fail Over Only
    3. Using the iSCSI Initiator tool, from the Targets tab 1 click on the Devices…​ button 2 :

      iscsi target tab2 mod
    4. From the Devices window, select a disk 1 and click the MPIO…​ button 2 :

      iscsi devices mpio mod
    5. The Device Details window displays the paths to each target portal. The Load Balancing Policy Fail Over Only must be selected.

      mpio set failover only mod
    6. View the multipath configuration from the PowerShell:

      mpclaim -s -d MPIO_DISK_ID

      Replace MPIO_DISK_ID with the appropriate disk identifier.

      Note

      There is one Active/Optimized path which is the path to the iSCSI gateway node that owns the LUN, and there is an Active/Unoptimized path for each other iSCSI gateway node.

      mpclaim output mod
  3. Optionally, tune the settings. Consider using the following registry settings:

    • Windows Disk Timeout

      Key

      HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Disk

      Value

      TimeOutValue = 65

    • Microsoft iSCSI Initiator Driver

      Key

      HKEY_LOCAL_MACHINE\\SYSTEM\CurrentControlSet\Control\Class\{4D36E97B-E325-11CE-BFC1-08002BE10318}\<Instance_Number>\Parameters

      Values

      LinkDownTime = 25
      SRBTimeoutDelta = 15

7.5.4. Configuring the iSCSI initiator for VMware ESXi

Prerequisites

  • VMware ESXi 6.5 and 6.7u3b using Virtual Machine compatibility 6.5 or 6.7 with VMFS 6
  • Access to the VMware Host Client
  • Root access to VMware ESXi host to execute the esxcli command

Procedure

  1. Disable HardwareAcceleratedMove (XCOPY):

    > esxcli system settings advanced set --int-value 0 --option /DataMover/HardwareAcceleratedMove
  2. Enable the iSCSI software. From the Navigator pane, click Storage 1 . Select the Adapters tab 2 . Click on Configure iSCSI 3 :

    esx web client storage main mod
  3. Verify the initiator name in the Name & alias section 1 .

    esx web client config iscsi main mod step2
  4. If the initiator name is different than the initiator name used when creating the client during the initial setup using gwcli, change the initiator name: From the VMware ESX host, use these esxcli commands.

    1. Get the adapter name for the iSCSI software:

      > esxcli iscsi adapter list
      > Adapter  Driver     State   UID            Description
      > -------  ---------  ------  -------------  ----------------------
      > vmhba64  iscsi_vmk  online  iscsi.vmhba64  iSCSI Software Adapter
    2. Set the initiator name:

      Syntax

      > esxcli iscsi adapter set -A ADAPTOR_NAME -n INITIATOR_NAME

      Example

      > esxcli iscsi adapter set -A vmhba64 -n iqn.1994-05.com.redhat:rh7-client

  5. Configure CHAP. Expand the CHAP authentication section 1 . Select “Do not use CHAP unless required by target” 2 . Enter the CHAP Name and Secret 3 credentials that were used in the initial setup. Verify the Mutual CHAP authentication section 4 has “Do not use CHAP” selected.

    esx web client chap mod step3
    Warning

    Due to a bug in the VMware Host Client, the CHAP settings are not used initially. On the Ceph iSCSI gateway node, the kernel logs include the following errors as an indication of this bug:

    > kernel: CHAP user or password not set for Initiator ACL
    > kernel: Security negotiation failed.
    > kernel: iSCSI Login negotiation failed.

    To work around this bug, configure the CHAP settings using the esxcli command. The authname argument is the Name in the vSphere Web Client:

    > esxcli iscsi adapter auth chap set --direction=uni --authname=myiscsiusername --secret=myiscsipassword --level=discouraged -A vmhba64
  6. Configure the iSCSI settings. Expand Advanced settings 1 . Set the RecoveryTimeout value to 25 2 .

    esx web client iscsi recovery timeout mod step4
  7. Set the discovery address. In the Dynamic targets section 1 , click Add dynamic target 2 . Under Address 3 add an IP addresses for one of the Ceph iSCSI gateways. Only one IP address needs to be added. Finally, click the Save configuration button 4 . From the main interface, on the Devices tab, you will see the RBD image.

    esx web client config iscsi main mod step5
    Note

    LUN is configured automatically, using the ALUA SATP and MRU PSP. Do not use other SATPs and PSPs. You can verify this by the esxcli command:

    Syntax

    esxcli storage nmp path list -d eui.DEVICE_ID

    Replace DEVICE_ID with the appropriate device identifier.

  8. Verify that multipathing has been set up correctly.

    1. List the devices:

      Example

      > esxcli storage nmp device list | grep iSCSI
         Device Display Name: LIO-ORG iSCSI Disk (naa.6001405f8d087846e7b4f0e9e3acd44b)
         Device Display Name: LIO-ORG iSCSI Disk (naa.6001405057360ba9b4c434daa3c6770c)

    2. Get the multipath information for the Ceph iSCSI disk from the previous step:

      Example

      > esxcli storage nmp path list -d naa.6001405f8d087846e7b4f0e9e3acd44b
      
      iqn.2005-03.com.ceph:esx1-00023d000001,iqn.2003-01.com.redhat.iscsi-gw:iscsi-igw,t,1-naa.6001405f8d087846e7b4f0e9e3acd44b
         Runtime Name: vmhba64:C0:T0:L0
         Device: naa.6001405f8d087846e7b4f0e9e3acd44b
         Device Display Name: LIO-ORG iSCSI Disk (naa.6001405f8d087846e7b4f0e9e3acd44b)
         Group State: active
         Array Priority: 0
         Storage Array Type Path Config: {TPG_id=1,TPG_state=AO,RTP_id=1,RTP_health=UP}
         Path Selection Policy Path Config: {current path; rank: 0}
      
      iqn.2005-03.com.ceph:esx1-00023d000002,iqn.2003-01.com.redhat.iscsi-gw:iscsi-igw,t,2-naa.6001405f8d087846e7b4f0e9e3acd44b
         Runtime Name: vmhba64:C1:T0:L0
         Device: naa.6001405f8d087846e7b4f0e9e3acd44b
         Device Display Name: LIO-ORG iSCSI Disk (naa.6001405f8d087846e7b4f0e9e3acd44b)
         Group State: active unoptimized
         Array Priority: 0
         Storage Array Type Path Config: {TPG_id=2,TPG_state=ANO,RTP_id=2,RTP_health=UP}
         Path Selection Policy Path Config: {non-current path; rank: 0}

      From the example output, each path has an iSCSI or SCSI name with the following parts:

      Initiator name = iqn.2005-03.com.ceph:esx1 ISID = 00023d000002 Target name = iqn.2003-01.com.redhat.iscsi-gw:iscsi-igw Target port group = 2 Device id = naa.6001405f8d087846e7b4f0e9e3acd44b

      The Group State value of active indicates this is the Active-Optimized path to the iSCSI gateway. The gwcli command lists the active as the iSCSI gateway owner. The rest of the paths have the Group State value of unoptimized and are the failover path, if the active path goes into a dead state.

  9. To match all paths to their respective iSCSI gateways:

    Example

    > esxcli iscsi session connection list
    vmhba64,iqn.2003-01.com.redhat.iscsi-gw:iscsi-igw,00023d000001,0
       Adapter: vmhba64
       Target: iqn.2003-01.com.redhat.iscsi-gw:iscsi-igw
       ISID: 00023d000001
       CID: 0
       DataDigest: NONE
       HeaderDigest: NONE
       IFMarker: false
       IFMarkerInterval: 0
       MaxRecvDataSegmentLength: 131072
       MaxTransmitDataSegmentLength: 262144
       OFMarker: false
       OFMarkerInterval: 0
       ConnectionAddress: 10.172.19.21
       RemoteAddress: 10.172.19.21
       LocalAddress: 10.172.19.11
       SessionCreateTime: 08/16/18 04:20:06
       ConnectionCreateTime: 08/16/18 04:20:06
       ConnectionStartTime: 08/16/18 04:30:45
       State: logged_in
    
    vmhba64,iqn.2003-01.com.redhat.iscsi-gw:iscsi-igw,00023d000002,0
       Adapter: vmhba64
       Target: iqn.2003-01.com.redhat.iscsi-gw:iscsi-igw
       ISID: 00023d000002
       CID: 0
       DataDigest: NONE
       HeaderDigest: NONE
       IFMarker: false
       IFMarkerInterval: 0
       MaxRecvDataSegmentLength: 131072
       MaxTransmitDataSegmentLength: 262144
       OFMarker: false
       OFMarkerInterval: 0
       ConnectionAddress: 10.172.19.22
       RemoteAddress: 10.172.19.22
       LocalAddress: 10.172.19.12
       SessionCreateTime: 08/16/18 04:20:06
       ConnectionCreateTime: 08/16/18 04:20:06
       ConnectionStartTime: 08/16/18 04:30:41
       State: logged_in

    Match the path name with the ISID value, and the RemoteAddress value is the IP address of the owning iSCSI gateway.

7.6. Managing iSCSI services

The ceph-iscsi package installs the configuration management logic, and the rbd-target-gw and rbd-target-api systemd services.

The rbd-target-api service restores the Linux iSCSI target state at startup, and responds to ceph-iscsi REST API calls from tools like gwcli and Red Hat Ceph Storage Dashboard. The rbd-target-gw service provides metrics using the Prometheus plug-in.

The rbd-target-api service assumes it is the only user of the Linux kernel’s target layer. Do not use the target service installed with the targetcli package when using rbd-target-api. Ansible automatically disables the targetcli target service during the Ceph iSCSI gateway installation.

Procedure

  1. To start the services:

    # systemctl start rbd-target-api
    # systemctl start rbd-target-gw
  2. To restart the services:

    # systemctl restart rbd-target-api
    # systemctl restart rbd-target-gw
  3. To reload the services:

    # systemctl reload rbd-target-api
    # systemctl reload rbd-target-gw

    The reload request forces rbd-target-api to reread the configuration and apply it to the current running environment. This is normally not required, because changes are deployed in parallel from Ansible to all iSCSI gateway nodes.

  4. To stop the services:

    # systemctl stop rbd-target-api
    # systemctl stop rbd-target-gw

    The stop request closes the gateway’s portal interfaces, dropping connections to clients and wipes the current Linux iSCSI target configuration from the kernel. This returns the iSCSI gateway to a clean state. When clients are disconnected, active I/O is rescheduled to the other iSCSI gateways by the client side multipathing layer.

7.7. Adding more iSCSI gateways

As a storage administrator, you can expand the initial two iSCSI gateways to four iSCSI gateways by using the gwcli command-line tool or the Red Hat Ceph Storage Dashboard. Adding more iSCSI gateways provides you more flexibility when using load-balancing and failover options, along with providing more redundancy.

7.7.1. Prerequisites

  • A running Red Hat Ceph Storage 4 cluster
  • Spare nodes or existing OSD nodes
  • root permissions

7.7.2. Using Ansible to add more iSCSI gateways

You can using the Ansible automation utility to add more iSCSI gateways. This procedure expands the default installation of two iSCSI gateways to four iSCSI gateways. You can configure the iSCSI gateway on a standalone node or it can be collocated with existing OSD nodes.

Prerequisites

  • Red Hat Enterprise Linux 7.7 or later.
  • A running Red Hat Ceph Storage cluster.
  • Installation of the iSCSI gateway software.
  • Having admin user access on the Ansible administration node.
  • Having root user access on the new nodes.

Procedure

  1. On the new iSCSI gateway nodes, enable the Red Hat Ceph Storage Tools repository:

    Red Hat Enterprise Linux 7

    [root@iscsigw ~]# subscription-manager repos --enable=rhel-7-server-rhceph-4-tools-rpms

    Red Hat Enterprise Linux 8

    [root@iscsigw ~]# subscription-manager repos --enable=rhceph-4-tools-for-rhel-8-x86_64-rpms

  2. Install the ceph-iscsi-config package:

    [root@iscsigw ~]# yum install ceph-iscsi-config
  3. Append to the list in /etc/ansible/hosts file for the gateway group:

    Example

    [iscsigws]
    ...
    ceph-igw-3
    ceph-igw-4

    Note

    If colocating the iSCSI gateway with an OSD node, add the OSD node to the [iscsigws] section.

  4. Change to the ceph-ansible directory:

    [admin@ansible ~]$ cd /usr/share/ceph-ansible
  5. On the Ansible administration node, run the appropriate Ansible playbook:

    • Bare-metal deployments:

      [admin@ansible ceph-ansible]$ ansible-playbook site.yml -i hosts
    • Container deployments:

      [admin@ansible ceph-ansible]$ ansible-playbook site-container.yml -i hosts
    Important

    Providing IP addresses for the gateway_ip_list option is required. You cannot use a mix of IPv4 and IPv6 addresses.

  6. From the iSCSI initiators, re-login to use the newly added iSCSI gateways.

Additional Resources

7.7.3. Using gwcli to add more iSCSI gateways

You can use the gwcli command-line tool to add more iSCSI gateways. This procedure expands the default of two iSCSI gateways to four iSCSI gateways.

Prerequisites

  • Red Hat Enterprise Linux 7.7 or later.
  • A running Red Hat Ceph Storage cluster.
  • Installation of the iSCSI gateway software.
  • Having root user access to the new nodes or OSD nodes.

Procedure

  1. If the Ceph iSCSI gateway is not colocated on an OSD node, copy the Ceph configuration files, located in the /etc/ceph/ directory, from a running Ceph node in the storage cluster to the new iSCSI Gateway node. The Ceph configuration files must exist on the iSCSI gateway node under the /etc/ceph/ directory.
  2. Install and configure the Ceph command-line interface.
  3. On the new iSCSI gateway nodes, enable the Red Hat Ceph Storage Tools repository:

    Red Hat Enterprise Linux 7

    [root@iscsigw ~]# subscription-manager repos --enable=rhel-7-server-rhceph-4-tools-rpms

    Red Hat Enterprise Linux 8

    [root@iscsigw ~]# subscription-manager repos --enable=rhceph-4-tools-for-rhel-8-x86_64-rpms

  4. Install the ceph-iscsi, and tcmu-runner packages:

    Red Hat Enterprise Linux 7

    [root@iscsigw ~]# yum install ceph-iscsi tcmu-runner

    Red Hat Enterprise Linux 8

    [root@iscsigw ~]# dnf install ceph-iscsi tcmu-runner

    1. If needed, install the openssl package:

      Red Hat Enterprise Linux 7

      [root@iscsigw ~]# yum install openssl

      Red Hat Enterprise Linux 8

      [root@iscsigw ~]# dnf install openssl

  5. On one of the existing iSCSI gateway nodes, edit the /etc/ceph/iscsi-gateway.cfg file and append the trusted_ip_list option with the new IP addresses for the new iSCSI gateway nodes. For example:

    [config]
    ...
    trusted_ip_list = 10.172.19.21,10.172.19.22,10.172.19.23,10.172.19.24
  6. Copy the updated /etc/ceph/iscsi-gateway.cfg file to all the iSCSI gateway nodes.

    Important

    The iscsi-gateway.cfg file must be identical on all iSCSI gateway nodes.

  7. Optionally, if using SSL, also copy the ~/ssl-keys/iscsi-gateway.crt, ~/ssl-keys/iscsi-gateway.pem, ~/ssl-keys/iscsi-gateway-pub.key, and ~/ssl-keys/iscsi-gateway.key files from one of the existing iSCSI gateway nodes to the /etc/ceph/ directory on the new iSCSI gateway nodes.
  8. Enable and start the API service on the new iSCSI gateway nodes:

    [root@iscsigw ~]# systemctl enable rbd-target-api
    [root@iscsigw ~]# systemctl start rbd-target-api
  9. Start the iSCSI gateway command-line interface:

    [root@iscsigw ~]# gwcli
  10. Creating the iSCSI gateways using either IPv4 or IPv6 addresses:

    Syntax

    >/iscsi-target create iqn.2003-01.com.redhat.iscsi-gw:_TARGET_NAME_
    > goto gateways
    > create ISCSI_GW_NAME IP_ADDR_OF_GW
    > create ISCSI_GW_NAME IP_ADDR_OF_GW

    Example

    >/iscsi-target create iqn.2003-01.com.redhat.iscsi-gw:ceph-igw
    > goto gateways
    > create ceph-gw-3 10.172.19.23
    > create ceph-gw-4 10.172.19.24

    Important

    You cannot use a mix of IPv4 and IPv6 addresses.

  11. From the iSCSI initiators, re-login to use the newly added iSCSI gateways.

Additional Resources

7.8. Verifying that the initiator is connected to the iSCSI target

After installing the iSCSI gateway and configuring the iSCSI target and an initiator, verify that the initiator is properly connected to the iSCSI target.

Prerequisites

  • Installation of the Ceph iSCSI gateway software.
  • Configured the iSCSI target.
  • Configured the iSCSI initiator.

Procedure

  1. Start the iSCSI gateway command-line interface:

    [root@iscsigw ~]# gwcli
  2. Verify that the initiator is connected the iSCSI target:

    /> goto hosts
    /iscsi-target...csi-igw/hosts> ls
    o- hosts .............................. [Hosts: 1: Auth: None]
      o- iqn.1994-05.com.redhat:rh7-client  [LOGGED-IN, Auth: None, Disks: 0(0.00Y)]

    The initiator status is LOGGED-IN if it is connected.

  3. Verify that LUNs are balanced across iSCSI gateways:

    /> goto hosts
    /iscsi-target...csi-igw/hosts> ls
    o- hosts ................................. [Hosts: 2: Auth: None]
      o- iqn.2005-03.com.ceph:esx ............ [Auth: None, Disks: 4(310G)]
      | o- lun 0 ............................. [rbd.disk_1(100G), Owner: ceph-gw-1]
      | o- lun 1 ............................. [rbd.disk_2(10G), Owner: ceph-gw-2]

    When creating a disk, the disk is assigned an iSCSI gateway as its Owner based on what gateways have the lowest number of mapped LUNs. If this number is balanced, gateways are assigned based on a round robin allocation. Currently, the balancing of LUNs is not dynamic and cannot be selected by the user.

    When the initiator is logged into the target, and the multipath layer is in a optimized state, the initiator’s operating system multipath utilities report the path to the Owner gateway as being in ALUA Active-Optimized (AO) state. The multipath utilities report the other paths as being in the ALUA Active-non-Optimized (ANO) state.

    If the AO path fails, one of the other iSCSI gateways is used. The ordering for the failover gateway depends on the initiator’s multipath layer, where normally, the order is based on which path was discovered first.

7.9. Upgrading the Ceph iSCSI gateway using Ansible

Upgrading the Red Hat Ceph Storage iSCSI gateways can be done by using an Ansible playbook designed for rolling upgrades.

Prerequisites

  • A running Ceph iSCSI gateway.
  • A running Red Hat Ceph Storage cluster.
  • Admin-level access to all nodes in the storage cluster.
Note

You can run the upgrade procedure as an administrative user or as root. If you want to run it as root, make sure that you have ssh set up for use with Ansible.

Procedure

  1. Verify that the correct iSCSI gateway nodes are listed in the Ansible inventory file (/etc/ansible/hosts).
  2. Run the rolling upgrade playbook:

    [admin@ansible ceph-ansible]$ ansible-playbook rolling_update.yml
  3. Run the appropriate playbook to finish the upgrade:

    Bare-metal deployments

    [admin@ansible ceph-ansible]$ ansible-playbook site.yml --limit iscsigws -i hosts

    Container deployments

    [admin@ansible ceph-ansible]$ ansible-playbook site-container.yml --limit iscsigws -i hosts

Additional Resources

7.10. Upgrading the Ceph iSCSI gateway using the command-line interface

Upgrading the Red Hat Ceph Storage iSCSI gateways can be done in a rolling fashion, by upgrading one bare-metal iSCSI gateway node at a time.

Warning

Do not upgrade the iSCSI gateway while upgrading and restarting Ceph OSDs. Wait until the OSD upgrades are finished and the storage cluster is in an active+clean state.

Prerequisites

  • A running Ceph iSCSI gateway.
  • A running Red Hat Ceph Storage cluster.
  • Having root access to the iSCSI gateway node.

Procedure

  1. Update the iSCSI gateway packages:

    [root@iscsigw ~]# yum update ceph-iscsi
  2. Stop the iSCSI gateway daemons:

    [root@iscsigw ~]# systemctl stop rbd-target-api
    [root@iscsigw ~]# systemctl stop rbd-target-gw
  3. Verify that the iSCSI gateway daemons stopped cleanly:

    [root@iscsigw ~]# systemctl status rbd-target-gw
    1. If the rbd-target-gw service successfully stops, then skip to step 4.
    2. If the rbd-target-gw service fails to stop, then do the following steps:

      1. If the targetcli package is not install, then install the targetcli package:

        [root@iscsigw ~]# yum install targetcli
      2. Check for existing target objects:

        [root@iscsigw ~]# targetcli ls

        Example

        o- / ............................................................. [...]
        o- backstores .................................................... [...]
        | o- user:rbd ..................................... [Storage Objects: 0]
        o- iscsi .................................................. [Targets: 0]

        If the backstores and Storage Objects are empty, then the iSCSI target has been shutdown cleanly and you can skip to step 4.

      3. If you have still have target objects, use the following command to force remove all target objects:

        [root@iscsigw ~]# targetcli clearconfig confirm=True
        Warning

        If multiple services are using the iSCSI target, use targetcli in interactive mode to delete those specific objects.

  4. Update the tcmu-runner package:

    [root@iscsigw ~]# yum update tcmu-runner
  5. Stop the tcmu-runner service:

    [root@iscsigw ~]# systemctl stop tcmu-runner
  6. Restart the iSCSI gateway services in the following order:

    [root@iscsigw ~]# systemctl start tcmu-runner
    [root@iscsigw ~]# systemctl start rbd-target-gw
    [root@iscsigw ~]# systemctl start rbd-target-api

7.11. Monitoring the iSCSI gateways

Red Hat provides an additional tool for Ceph iSCSI gateway environments to monitor performance of exported Ceph block device (RBD) images.

The gwtop tool is a top-like tool that displays aggregated performance metrics of RBD images that are exported to clients over iSCSI. The metrics are sourced from a Performance Metrics Domain Agent (PMDA). Information from the Linux-IO target (LIO) PMDA is used to list each exported RBD image with the connected client and its associated I/O metrics.

Note

The gwtop tool is not available in containerized environments. This means that the Performance Co-Pilot (PCP) packages are also unavailable for containerized environments.

The following procedure is done on the iSCSI gateway nodes.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Installation of the Ceph iSCSI gateway software.
  • Root-level access to the Ceph iSCSI gateway nodes.

Procedure

  1. Install the ceph-iscsi-tools package:

    [root@iscsigw ~]# yum install ceph-iscsi-tools
  2. Install the performance co-pilot package:

    [root@iscsigw ~]# yum install pcp
  3. Install the LIO PMDA package:

    [root@iscsigw ~]# yum install pcp-pmda-lio
  4. Enable and start the performance co-pilot service:

    [root@iscsigw ~]# systemctl enable pmcd
    [root@iscsigw ~]# systemctl start pmcd
  5. Register the pcp-pmda-lio agent:

    [root@iscsigw ~]# cd /var/lib/pcp/pmdas/lio
    [root@iscsigw ~]# ./Install

    By default, gwtop assumes the iSCSI gateway configuration object is stored in a RADOS object called gateway.conf in the rbd pool. This configuration defines the iSCSI gateways to contact for gathering the performance statistics. You can override this setup by using the -g or -c flags. See gwtop --help for more details.

    The LIO configuration determines which type of performance statistics to extract from performance co-pilot. When gwtop starts it looks at the LIO configuration, and if it find user-space disks, gwtop selects the LIO collector automatically.

  6. Use the gwtop utility to monitor the iSCSI gateways. For user backed storage (TCMU) devices:

    gwtop  2/2 Gateways   CPU% MIN:  4 MAX:  5    Network Total In:    2M  Out:    3M   10:20:00
    Capacity:   8G    Disks:   8   IOPS:  503   Clients:  1   Ceph: HEALTH_OK          OSDs:   3
    Pool.Image       Src    Size     iops     rMB/s     wMB/s   Client
    iscsi.t1703             500M        0      0.00      0.00
    iscsi.testme1           500M        0      0.00      0.00
    iscsi.testme2           500M        0      0.00      0.00
    iscsi.testme3           500M        0      0.00      0.00
    iscsi.testme5           500M        0      0.00      0.00
    rbd.myhost_1      T       4G      504      1.95      0.00   rh460p(CON)
    rbd.test_2                1G        0      0.00      0.00
    rbd.testme              500M        0      0.00      0.00

    In the Client column, (CON) means the iSCSI initiator (client) is currently logged into the iSCSI gateway. If -multi- is displayed, then multiple clients are mapped to the single RBD image.

    Warning

    SCSI persistent reservations are not supported. Mapping multiple iSCSI initiators to an RBD image is supported, if using a cluster aware file system or clustering software that does not rely on SCSI persistent reservations. For example, VMware vSphere environments using ATS is supported, but using Microsoft’s clustering server (MSCS) is not supported.

Additional Resources

  • For details how to monitor iSCSI gateways using the Red Hat Ceph Storage Dashboard, see the iSCSI functions section in the Red Hat Ceph Storage Dashboard Guide.
  • For details about the Performance Co-Pilot (PCP) application, see the Monitoring performance with Performance Co-Pilot chapter in the Monitoring and managing system status and performance guide for Red Hat Enterprise Linux 8.

7.12. Removing the iSCSI configuration

To remove the iSCSI configuration, use the gwcli utility to remove hosts and disks, and the Ansible purge-iscsi-gateways.yml playbook to remove the iSCSI target configuration.

Warning

Using the purge-iscsi-gateways.yml playbook is a destructive action against the iSCSI gateway environment.

+ WARNING: An attempt to use purge-iscsi-gateways.yml fails if RBD images have snapshots or clones and are exported through the Ceph iSCSI gateway.

Prerequisites

  • Disconnect all iSCSI initiators:

    • Red Hat Enterprise Linux initiators:

      Syntax

      iscsiadm -m node -T TARGET_NAME --logout

      Replace TARGET_NAME with the configured iSCSI target name, for example:

      Example

      # iscsiadm -m node -T iqn.2003-01.com.redhat.iscsi-gw:ceph-igw --logout
      Logging out of session [sid: 1, target: iqn.2003-01.com.redhat.iscsi-gw:iscsi-igw, portal: 10.172.19.21,3260]
      Logging out of session [sid: 2, target: iqn.2003-01.com.redhat.iscsi-gw:iscsi-igw, portal: 10.172.19.22,3260]
      Logout of [sid: 1, target: iqn.2003-01.com.redhat.iscsi-gw:iscsi-igw, portal: 10.172.19.21,3260] successful.
      Logout of [sid: 2, target: iqn.2003-01.com.redhat.iscsi-gw:iscsi-igw, portal: 10.172.19.22,3260] successful.

    • Windows initiators:

      See the Microsoft documentation for more details.

    • VMware ESXi initiators:

      See the VMware documentation for more details.

Procedure

  1. Run the iSCSI gateway command line utility:

    [root@iscsigw ~]# gwcli
  2. Remove the hosts:

    Syntax

    /> cd /iscsi-target/iqn.2003-01.com.redhat.iscsi-gw:$TARGET_NAME/hosts
    /> /iscsi-target...TARGET_NAME/hosts> delete CLIENT_NAME

    Replace TARGET_NAME with the configured iSCSI target name, and replace CLIENT_NAME with iSCSI initiator name, for example:

    Example

    /> cd /iscsi-target/iqn.2003-01.com.redhat.iscsi-gw:ceph-igw/hosts
    /> /iscsi-target...eph-igw/hosts> delete iqn.1994-05.com.redhat:rh7-client

  3. Remove the disks:

    Syntax

    /> cd /disks/
    /disks> delete POOL_NAME.IMAGE_NAME

    Replace POOL_NAME with the name of the pool and the IMAGE_NAME with the name of the image, for example:

    Example

    /> cd /disks/
    /disks> delete rbd.disk_1

  4. Run the iSCSI gateway purge Ansible playbook:

    [root@ansible ~]# cd /usr/share/ceph-ansible/
    [root@ansible ceph-ansible]# ansible-playbook purge-iscsi-gateways.yml
  5. Enter the type of purge when prompted:

    lio
    In this mode the Linux iSCSI target configuration is purged on all iSCSI gateways that are defined. Disks that were created are left untouched within the Ceph storage cluster.
    all
    When all is chosen, the Linux iSCSI target configuration is removed together with all RBD images that were defined within the iSCSI gateway environment, other unrelated RBD images will not be removed. Be sure to chose the correct mode because this operation deletes data.

    Example

    [root@rh7-iscsi-client ceph-ansible]# ansible-playbook purge-iscsi-gateways.yml
    Which configuration elements should be purged? (all, lio or abort) [abort]: all
    
    
    PLAY [Confirm removal of the iSCSI gateway configuration] *********************
    
    
    GATHERING FACTS ***************************************************************
    ok: [localhost]
    
    
    TASK: [Exit playbook if user aborted the purge] *******************************
    skipping: [localhost]
    
    
    TASK: [set_fact ] *************************************************************
    ok: [localhost]
    
    
    PLAY [Removing the gateway configuration] *************************************
    
    
    GATHERING FACTS ***************************************************************
    ok: [ceph-igw-1]
    ok: [ceph-igw-2]
    
    
    TASK: [igw_purge | purging the gateway configuration] *************************
    changed: [ceph-igw-1]
    changed: [ceph-igw-2]
    
    
    TASK: [igw_purge | deleting configured rbd devices] ***************************
    changed: [ceph-igw-1]
    changed: [ceph-igw-2]
    
    
    PLAY RECAP ********************************************************************
    ceph-igw-1                 : ok=3    changed=2    unreachable=0    failed=0
    ceph-igw-2                 : ok=3    changed=2    unreachable=0    failed=0
    localhost                  : ok=2    changed=0    unreachable=0    failed=0

7.13. Additional Resources

  • For details on managing iSCSI gateway using the Red Hat Ceph Storage Dashboard, see the iSCSI functions section in the Dashboard Guide for Red Hat Ceph Storage 4

Appendix A. Ceph block device configuration reference

As a storage administrator, you can fine tune the behavior of Ceph block devices through the various options that are available. You can use this reference for viewing such things as the default Ceph block device options, and Ceph block device caching options.

A.1. Prerequisites

  • A running Red Hat Ceph Storage cluster.

A.2. Block device default options

It is possible to override the default settings for creating an image. Ceph will create images with format 2 and no striping.

rbd_default_format
Description
The default format (2) if no other format is specified. Format 1 is the original format for a new image, which is compatible with all versions of librbd and the kernel module, but does not support newer features like cloning. Format 2 is supported by librbd and the kernel module since version 3.11 (except for striping). Format 2 adds support for cloning and is more easily extensible to allow more features in the future.
Type
Integer
Default
2
rbd_default_order
Description
The default order if no other order is specified.
Type
Integer
Default
22
rbd_default_stripe_count
Description
The default stripe count if no other stripe count is specified. Changing the default value requires striping v2 feature.
Type
64-bit Unsigned Integer
Default
0
rbd_default_stripe_unit
Description
The default stripe unit if no other stripe unit is specified. Changing the unit from 0 (that is, the object size) requires the striping v2 feature.
Type
64-bit Unsigned Integer
Default
0
rbd_default_features
Description

The default features enabled when creating an block device image. This setting only applies to format 2 images. The settings are:

1: Layering support. Layering enables you to use cloning.

2: Striping v2 support. Striping spreads data across multiple objects. Striping helps with parallelism for sequential read/write workloads.

4: Exclusive locking support. When enabled, it requires a client to get a lock on an object before making a write.

8: Object map support. Block devices are thin provisioned—​meaning, they only store data that actually exists. Object map support helps track which objects actually exist (have data stored on a drive). Enabling object map support speeds up I/O operations for cloning, or importing and exporting a sparsely populated image.

16: Fast-diff support. Fast-diff support depends on object map support and exclusive lock support. It adds another property to the object map, which makes it much faster to generate diffs between snapshots of an image, and the actual data usage of a snapshot much faster.

32: Deep-flatten support. Deep-flatten makes rbd flatten work on all the snapshots of an image, in addition to the image itself. Without it, snapshots of an image will still rely on the parent, so the parent will not be delete-able until the snapshots are deleted. Deep-flatten makes a parent independent of its clones, even if they have snapshots.

64: Journaling support. Journaling records all modifications to an image in the order they occur. This ensures that a crash-consistent mirror of the remote image is available locally

The enabled features are the sum of the numeric settings.

Type
Integer
Default

61 - layering, exclusive-lock, object-map, fast-diff, and deep-flatten are enabled

Important

The current default setting is not compatible with the RBD kernel driver nor older RBD clients.

rbd_default_map_options
Description
Most of the options are useful mainly for debugging and benchmarking. See man rbd under Map Options for details.
Type
String
Default
""

A.3. Block device general options

rbd_op_threads
Description
The number of block device operation threads.
Type
Integer
Default
1
Warning

Do not change the default value of rbd_op_threads because setting it to a number higher than 1 might cause data corruption.

rbd_op_thread_timeout
Description
The timeout (in seconds) for block device operation threads.
Type
Integer
Default
60
rbd_non_blocking_aio
Description
If true, Ceph will process block device asynchronous I/O operations from a worker thread to prevent blocking.
Type
Boolean
Default
true
rbd_concurrent_management_ops
Description
The maximum number of concurrent management operations in flight (for example, deleting or resizing an image).
Type
Integer
Default
10
rbd_request_timed_out_seconds
Description
The number of seconds before a maintenance request times out.
Type
Integer
Default
30
rbd_clone_copy_on_read
Description
When set to true, copy-on-read cloning is enabled.
Type
Boolean
Default
false
rbd_enable_alloc_hint
Description
If true, allocation hinting is enabled, and the block device will issue a hint to the OSD back end to indicate the expected size object.
Type
Boolean
Default
true
rbd_skip_partial_discard
Description
If true, the block device will skip zeroing a range when trying to discard a range inside an object.
Type
Boolean
Default
false
rbd_tracing
Description
Set this option to true to enable the Linux Trace Toolkit Next Generation User Space Tracer (LTTng-UST) tracepoints. See Tracing RADOS Block Device (RBD) Workloads with the RBD Replay Feature for details.
Type
Boolean
Default
false
rbd_validate_pool
Description
Set this option to true to validate empty pools for RBD compatibility.
Type
Boolean
Default
true
rbd_validate_names
Description
Set this option to true to validate image specifications.
Type
Boolean
Default
true

A.4. Block device caching options

The user space implementation of the Ceph block device, that is, librbd, cannot take advantage of the Linux page cache, so it includes its own in-memory caching, called RBD caching. Ceph block device caching behaves just like well-behaved hard disk caching. When the operating system sends a barrier or a flush request, all dirty data is written to the Ceph OSDs. This means that using write-back caching is just as safe as using a well-behaved physical hard disk with a virtual machine that properly sends flushes, that is, Linux kernel version 2.6.32 or higher. The cache uses a Least Recently Used (LRU) algorithm, and in write-back mode it can coalesce contiguous requests for better throughput.

Ceph block devices support write-back caching. To enable write-back caching, set rbd_cache = true to the [client] section of the Ceph configuration file. By default, librbd does not perform any caching. Writes and reads go directly to the storage cluster, and writes return only when the data is on disk on all replicas. With caching enabled, writes return immediately, unless there are more than rbd_cache_max_dirty unflushed bytes. In this case, the write triggers write-back and blocks until enough bytes are flushed.

Ceph block devices support write-through caching. You can set the size of the cache, and you can set targets and limits to switch from write-back caching to write-through caching. To enable write-through mode, set rbd_cache_max_dirty to 0. This means writes return only when the data is on disk on all replicas, but reads may come from the cache. The cache is in memory on the client, and each Ceph block device image has its own. Since the cache is local to the client, there is no coherency if there are others accessing the image. Running other file systems, such as GFS or OCFS, on top of Ceph block devices will not work with caching enabled.

The Ceph configuration settings for Ceph block devices must be set in the [client] section of the Ceph configuration file, by default, /etc/ceph/ceph.conf.

The settings include:

rbd_cache
Description
Enable caching for RADOS Block Device (RBD).
Type
Boolean
Required
No
Default
true
rbd_cache_size
Description
The RBD cache size in bytes.
Type
64-bit Integer
Required
No
Default
32 MiB
rbd_cache_max_dirty
Description
The dirty limit in bytes at which the cache triggers write-back. If 0, uses write-through caching.
Type
64-bit Integer
Required
No
Constraint
Must be less than rbd cache size.
Default
24 MiB
rbd_cache_target_dirty
Description
The dirty target before the cache begins writing data to the data storage. Does not block writes to the cache.
Type
64-bit Integer
Required
No
Constraint
Must be less than rbd cache max dirty.
Default
16 MiB
rbd_cache_max_dirty_age
Description
The number of seconds dirty data is in the cache before writeback starts.
Type
Float
Required
No
Default
1.0
rbd_cache_max_dirty_object
Description
The dirty limit for objects - set to 0 for auto calculate from rbd_cache_size.
Type
Integer
Default
0
rbd_cache_block_writes_upfront
Description
If true, it will block writes to the cache before the aio_write call completes. If false, it will block before the aio_completion is called.
Type
Boolean
Default
false
rbd_cache_writethrough_until_flush
Description
Start out in write-through mode, and switch to write-back after the first flush request is received. Enabling this is a conservative but safe setting in case VMs running on rbd are too old to send flushes, like the virtio driver in Linux before 2.6.32.
Type
Boolean
Required
No
Default
true

A.5. Block device parent and child read options

rbd_balance_snap_reads
Description
Ceph typically reads objects from the primary OSD. Since reads are immutable, you may enable this feature to balance snap reads between the primary OSD and the replicas.
Type
Boolean
Default
false
rbd_localize_snap_reads
Description
Whereas rbd_balance_snap_reads will randomize the replica for reading a snapshot. If you enable rbd_localize_snap_reads, the block device will look to the CRUSH map to find the closest or local OSD for reading the snapshot.
Type
Boolean
Default
false
rbd_balance_parent_reads
Description
Ceph typically reads objects from the primary OSD. Since reads are immutable, you may enable this feature to balance parent reads between the primary OSD and the replicas.
Type
Boolean
Default
false
rbd_localize_parent_reads
Description
Whereas rbd_balance_parent_reads will randomize the replica for reading a parent. If you enable rbd_localize_parent_reads, the block device will look to the CRUSH map to find the closest or local OSD for reading the parent.
Type
Boolean
Default
true

A.6. Block device read ahead options

RBD supports read-ahead/prefetching to optimize small, sequential reads. This should normally be handled by the guest OS in the case of a VM, but boot loaders may not issue efficient reads. Read-ahead is automatically disabled if caching is disabled.

rbd_readahead_trigger_requests
Description
Number of sequential read requests necessary to trigger read-ahead.
Type
Integer
Required
No
Default
10
rbd_readahead_max_bytes
Description
Maximum size of a read-ahead request. If zero, read-ahead is disabled.
Type
64-bit Integer
Required
No
Default
512 KiB
rbd_readahead_disable_after_bytes
Description
After this many bytes have been read from an RBD image, read-ahead is disabled for that image until it is closed. This allows the guest OS to take over read-ahead once it is booted. If zero, read-ahead stays enabled.
Type
64-bit Integer
Required
No
Default
50 MiB

A.7. Block device blacklist options

rbd_blacklist_on_break_lock
Description
Whether to blacklist clients whose lock was broken.
Type
Boolean
Default
true
rbd_blacklist_expire_seconds
Description
The number of seconds to blacklist - set to 0 for OSD default.
Type
Integer
Default
0

A.8. Block device journal options

rbd_journal_order
Description
The number of bits to shift to compute the journal object maximum size. The value is between 12 and 64.
Type
32-bit Unsigned Integer
Default
24
rbd_journal_splay_width
Description
The number of active journal objects.
Type
32-bit Unsigned Integer
Default
4
rbd_journal_commit_age
Description
The commit time interval in seconds.
Type
Double Precision Floating Point Number
Default
5
rbd_journal_object_flush_interval
Description
The maximum number of pending commits per a journal object.
Type
Integer
Default
0
rbd_journal_object_flush_bytes
Description
The maximum number of pending bytes per a journal object.
Type
Integer
Default
0
rbd_journal_object_flush_age
Description
The maximum time interval in seconds for pending commits.
Type
Double Precision Floating Point Number
Default
0
rbd_journal_pool
Description
Specifies a pool for journal objects.
Type
String
Default
""

A.9. Block device configuration override options

Block device configuration override options for global and pool levels.

Global level

Available keys

rbd_qos_bps_burst
Description
The desired burst limit of IO bytes.
Type
Integer
Default
0
rbd_qos_bps_limit
Description
The desired limit of IO bytes per second.
Type
Integer
Default
0
rbd_qos_iops_burst
Description
The desired burst limit of IO operations.
Type
Integer
Default
0
rbd_qos_iops_limit
Description
The desired limit of IO operations per second.
Type
Integer
Default
0
rbd_qos_read_bps_burst
Description
The desired burst limit of read bytes.
Type
Integer
Default
0
rbd_qos_read_bps_limit
Description
The desired limit of read bytes per second.
Type
Integer
Default
0
rbd_qos_read_iops_burst
Description
The desired burst limit of read operations.
Type
Integer
Default
0
rbd_qos_read_iops_limit
Description
The desired limit of read operations per second.
Type
Integer
Default
0
rbd_qos_write_bps_burst
Description
The desired burst limit of write bytes.
Type
Integer
Default
0
rbd_qos_write_bps_limit
Description
The desired limit of write bytes per second.
Type
Integer
Default
0
rbd_qos_write_iops_burst
Description
The desired burst limit of write operations.
Type
Integer
Default
0
rbd_qos_write_iops_limit
Description
The desired burst limit of write operations per second.
Type
Integer
Default
0

The above keys can be used for the following:

rbd config global set CONFIG_ENTITY KEY VALUE
Description
Set a global level configuration override.
rbd config global get CONFIG_ENTITY KEY
Description
Get a global level configuration override.
rbd config global list CONFIG_ENTITY
Description
List the global level configuration overrides.
rbd config global remove CONFIG_ENTITY KEY
Description
Remove a global level configuration override.

Pool level

rbd config pool set POOL_NAME KEY VALUE
Description
Set a pool level configuration override.
rbd config pool get POOL_NAME KEY
Description
Get a pool level configuration override.
rbd config pool list POOL_NAME
Description
List the pool level configuration overrides.
rbd config pool remove POOL_NAME KEY
Description
Remove a pool level configuration override.
Note

CONFIG_ENTITY is global, client or client id. KEY is the config key. VALUE is the config value. POOL_NAME is the name of the pool.

Appendix B. iSCSI Gateway Variables

iSCSI Gateway General Variables

seed_monitor
Purpose
Each iSCSI gateway needs access to the Ceph storage cluster for RADOS and RBD calls. This means the iSCSI gateway must have an appropriate /etc/ceph/ directory defined. The seed_monitor host is used to populate the iSCSI gateway’s /etc/ceph/ directory.
gateway_keyring
Purpose
Define a custom keyring name.
perform_system_checks
Purpose
This is a Boolean value that checks for multipath and LVM configuration settings on each iSCSI gateway. It must be set to true for at least the first run to ensure the multipathd daemon and LVM are configured properly.

iSCSI Gateway RBD-TARGET-API Variables

api_user
Purpose
The user name for the API. The default is admin.
api_password
Purpose
The password for using the API. The default is admin.
api_port
Purpose
The TCP port number for using the API. The default is 5000.
api_secure
Purpose
Value can be true or false. The default is false.
loop_delay
Purpose
Controls the sleeping interval in seconds for polling the iSCSI management object. The default value is 1.
trusted_ip_list
Purpose
A list of IPv4 or IPv6 addresses that have access to the API. By default, only the iSCSI gateway nodes have access.

Appendix C. Sample iscsigws.yml file

# Variables here are applicable to all host groups NOT roles

# This sample file generated by generate_group_vars_sample.sh

# Dummy variable to avoid error because ansible does not recognize the
# file as a good configuration file when no variable in it.
dummy:

# You can override vars by using host or group vars

###########
# GENERAL #
###########
# Whether or not to generate secure certificate to iSCSI gateway nodes
#generate_crt: False

#iscsi_conf_overrides: {}
#iscsi_pool_name: rbd
#iscsi_pool_size: "{{ osd_pool_default_size }}"

#copy_admin_key: True

##################
# RBD-TARGET-API #
##################
# Optional settings related to the CLI/API service
#api_user: admin
#api_password: admin
#api_port: 5000
#api_secure: false
#loop_delay: 1
#trusted_ip_list: 192.168.122.1


##########
# DOCKER #
##########

# Resource limitation
# For the whole list of limits you can apply see: docs.docker.com/engine/admin/resource_constraints
# Default values are based from: https://access.redhat.com/documentation/en-us/red_hat_ceph_storage/2/html/red_hat_ceph_storage_hardware_guide/minimum_recommendations
# These options can be passed using the 'ceph_mds_docker_extra_env' variable.

# TCMU_RUNNER resource limitation
#ceph_tcmu_runner_docker_memory_limit: "{{ ansible_memtotal_mb }}m"
#ceph_tcmu_runner_docker_cpu_limit: 1

# RBD_TARGET_GW resource limitation
#ceph_rbd_target_gw_docker_memory_limit: "{{ ansible_memtotal_mb }}m"
#ceph_rbd_target_gw_docker_cpu_limit: 1

# RBD_TARGET_API resource limitation
#ceph_rbd_target_api_docker_memory_limit: "{{ ansible_memtotal_mb }}m"
#ceph_rbd_target_api_docker_cpu_limit: 1

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