File System Guide

Red Hat Ceph Storage 4

Configuring and Mounting Ceph File Systems

Red Hat Ceph Storage Documentation Team

Abstract

This guide describes how to configure the Ceph Metadata Server (MDS) and how to create, mount and work the Ceph File System (CephFS).
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 the Ceph File System

As a storage administrator, you can gain an understanding of the features, system components, and limitations to manage a Ceph File System (CephFS) environment.

1.1. Ceph File System features and enhancements

The Ceph File System (CephFS) is a file system compatible with POSIX standards that is built on top of Ceph’s distributed object store, called RADOS (Reliable Autonomic Distributed Object Storage). CephFS provides file access to a Red Hat Ceph Storage cluster, and uses the POSIX semantics wherever possible. For example, in contrast to many other common network file systems like NFS, CephFS maintains strong cache coherency across clients. The goal is for processes using the file system to behave the same when they are on different hosts as when they are on the same host. However, in some cases, CephFS diverges from the strict POSIX semantics.

The Ceph File System has the following features and enhancements:

Scalability
The Ceph File System is highly scalable due to horizontal scaling of metadata servers and direct client reads and writes with individual OSD nodes.
Shared File System
The Ceph File System is a shared file system so multiple clients can work on the same file system at once.
High Availability
The Ceph File System provides a cluster of Ceph Metadata Servers (MDS). One is active and others are in standby mode. If the active MDS terminates unexpectedly, one of the standby MDS becomes active. As a result, client mounts continue working through a server failure. This behavior makes the Ceph File System highly available. In addition, you can configure multiple active metadata servers.
Configurable File and Directory Layouts
The Ceph File System allows users to configure file and directory layouts to use multiple pools, pool namespaces, and file striping modes across objects.
POSIX Access Control Lists (ACL)
The Ceph File System supports the POSIX Access Control Lists (ACL). ACL are enabled by default with the Ceph File Systems mounted as kernel clients with kernel version kernel-3.10.0-327.18.2.el7 or newer. To use an ACL with the Ceph File Systems mounted as FUSE clients, you must enable them.
Client Quotas
The Ceph File System supports setting quotas on any directory in a system. The quota can restrict the number of bytes or the number of files stored beneath that point in the directory hierarchy. CephFS client quotas are enabled by default.
Resizing
The Ceph File System size is only bound by the capacity of the OSDs servicing its data pool. To increase the capacity, add more OSDs to the CephFS data pool. To decrease the capacity, use either client quotas or pool quotas.
Snapshots
The Ceph File System supports read-only snapshots but not writable clones.
POSIX file system operations

The Ceph File System supports standard and consistent POSIX file system operations including the following access patterns:

  • Buffered write operations via the Linux page cache.
  • Cached read operations via the Linux page cache.
  • Direct I/O asynchronous or synchronous read/write operations, bypassing the page cache.
  • Memory mapped I/O.

Additional Resources

1.2. Ceph File System components

The Ceph File System has two primary components:

Clients
The CephFS clients perform I/O operations on behalf of applications using CephFS, such as, ceph-fuse for FUSE clients and kcephfs for kernel clients. CephFS clients send metadata requests to an active Metadata Server. In return, the CephFS client learns of the file metadata, and can begin safely caching both metadata and file data.
Metadata Servers (MDS)

The MDS does the following:

  • Provides metadata to CephFS clients.
  • Manages metadata related to files stored on the Ceph File System.
  • Coordinates access to the shared Red Hat Ceph Storage cluster.
  • Caches hot metadata to reduce requests to the backing metadata pool store.
  • Manages the CephFS clients' caches to maintain cache coherence.
  • Replicates hot metadata between active MDS.
  • Coalesces metadata mutations to a compact journal with regular flushes to the backing metadata pool.
  • CephFS requires at least one Metadata Server daemon (ceph-mds) to run.

The diagram below shows the component layers of the Ceph File System.

diag 32649267491e14479f8e4e6787ceb008

The bottom layer represents the underlying core storage cluster components:

  • Ceph OSDs (ceph-osd) where the Ceph File System data and metadata are stored.
  • Ceph Metadata Servers (ceph-mds) that manages Ceph File System metadata.
  • Ceph Monitors (ceph-mon) that manages the master copy of the cluster map.

The Ceph Storage protocol layer represents the Ceph native librados library for interacting with the core storage cluster.

The CephFS library layer includes the CephFS libcephfs library that works on top of librados and represents the Ceph File System.

The top layer represents two types of Ceph clients that can access the Ceph File Systems.

The diagram below shows more details on how the Ceph File System components interact with each other.

cephfs architecture

Additional Resources

1.3. Ceph File System and SELinux

Starting with Red Hat Enterprise Linux 8.3 and Red Hat Ceph Storage 4.2, support for using Security-Enhanced Linux (SELinux) on Ceph File Systems (CephFS) environments is available. You can now set any SELinux file type with CephFS, along with assigning a particular SELinux type on individual files. This support applies to the Ceph File System Metadata Server (MDS), the CephFS File System in User Space (FUSE) clients, and the CephFS kernel clients.

Additional Resources

1.4. Ceph File System limitations and the POSIX standards

Creation of multiple Ceph File Systems on one Red Hat Ceph Storage cluster is disabled by default. An attempt to create an additional Ceph File System fails with the following error message:

Error EINVAL: Creation of multiple filesystems is disabled.
Important

While technically possible, Red Hat does not support having multiple Ceph File Systems on one Red Hat Ceph Storage cluster. Doing so can cause the MDS or CephFS client nodes to terminate unexpectedly.

The Ceph File System diverges from the strict POSIX semantics in the following ways:

  • If a client’s attempt to write a file fails, the write operations are not necessarily atomic. That is, the client might call the write() system call on a file opened with the O_SYNC flag with an 8MB buffer and then terminates unexpectedly and the write operation can be only partially applied. Almost all file systems, even local file systems, have this behavior.
  • In situations when the write operations occur simultaneously, a write operation that exceeds object boundaries is not necessarily atomic. For example, writer A writes "aa|aa" and writer B writes "bb|bb" simultaneously, where "|" is the object boundary, and "aa|bb" is written rather than the proper "aa|aa" or "bb|bb".
  • POSIX includes the telldir() and seekdir() system calls that allow you to obtain the current directory offset and seek back to it. Because CephFS can fragment directories at any time, it is difficult to return a stable integer offset for a directory. As such, calling the seekdir() system call to a non-zero offset might often work but is not guaranteed to do so. Calling seekdir() to offset 0 will always work. This is an equivalent to the rewinddir() system call.
  • Sparse files propagate incorrectly to the st_blocks field of the stat() system call. CephFS does not explicitly track parts of a file that are allocated or written to, because the st_blocks field is always populated by the quotient of file size divided by block size. This behavior causes utilities, such as du, to overestimate used space.
  • When the mmap() system call maps a file into memory on multiple hosts, write operations are not coherently propagated to caches of other hosts. That is, if a page is cached on host A, and then updated on host B, host A page is not coherently invalidated.
  • CephFS clients present a hidden .snap directory that is used to access, create, delete, and rename snapshots. Although this directory is excluded from the readdir() system call, any process that tries to create a file or directory with the same name returns an error. The name of this hidden directory can be changed at mount time with the -o snapdirname=.<new_name> option or by using the client_snapdir configuration option.

Additional Resources

1.5. Additional Resources

  • See the Installing Metadata Servers section in the Red Hat Ceph Storage Installation Guide for more details.
  • If you want to use NFS Ganesha as an interface to the Ceph File System with Red Hat OpenStack Platform, see the CephFS with NFS-Ganesha deployment section in the Deploying the Shared File Systems service with CephFS through NFS guide for instructions on how to deploy such an environment.

Chapter 2. The Ceph File System Metadata Server

As a storage administrator, you can learn about the different states of the Ceph File System (CephFS) Metadata Server (MDS), along with learning about CephFS MDS ranking mechanic, configuring the MDS standby daemon, and cache size limits. Knowing these concepts can enable you to configure the MDS daemons for a storage environment.

2.1. Prerequisites

  • A running, and healthy Red Hat Ceph Storage cluster.
  • Installation of the Ceph Metadata Server daemons (ceph-mds).

2.2. Metadata Server daemon states

The Metadata Server (MDS) daemons operate in two states:

  • Active — manages metadata for files and directories stores on the Ceph File System.
  • Standby — serves as a backup, and becomes active when an active MDS daemon becomes unresponsive.

By default, a Ceph File System uses only one active MDS daemon. However, systems with many clients benefit from multiple active MDS daemons.

You can configure the file system to use multiple active MDS daemons so that you can scale metadata performance for larger workloads. The active MDS daemons dynamically share the metadata workload when metadata load patterns change. Note that systems with multiple active MDS daemons still require standby MDS daemons to remain highly available.

What Happens When the Active MDS Daemon Fails

When the active MDS becomes unresponsive, a Ceph Monitor daemon waits a number of seconds equal to the value specified in the mds_beacon_grace option. If the active MDS is still unresponsive after the specified time period has passed, the Ceph Monitor marks the MDS daemon as laggy. One of the standby daemons becomes active, depending on the configuration.

Note

To change the value of mds_beacon_grace, add this option to the Ceph configuration file and specify the new value.

2.3. Metadata Server ranks

Each Ceph File System (CephFS) has a number of ranks, one by default, which starts at zero.

Ranks define the way how the metadata workload is shared between multiple Metadata Server (MDS) daemons. The number of ranks is the maximum number of MDS daemons that can be active at one time. Each MDS daemon handles a subset of the CephFS metadata that is assigned to that rank.

Each MDS daemon initially starts without a rank. The Ceph Monitor assigns a rank to the daemon. The MDS daemon can only hold one rank at a time. Daemons only lose ranks when they are stopped.

The max_mds setting controls how many ranks will be created.

The actual number of ranks in the CephFS is only increased if a spare daemon is available to accept the new rank.

Rank States

Ranks can be:

  • Up - A rank that is assigned to the MDS daemon.
  • Failed - A rank that is not associated with any MDS daemon.
  • Damaged - A rank that is damaged; its metadata is corrupted or missing. Damaged ranks are not assigned to any MDS daemons until the operator fixes the problem, and uses the ceph mds repaired command on the damaged rank.

2.4. Metadata Server cache size limits

You can limit the size of the Ceph File System (CephFS) Metadata Server (MDS) cache by:

  • A memory limit: Use the mds_cache_memory_limit option. IMPORTANT: Red Hat recommends to use memory limits instead of inode count limits.
  • Inode count: Use the mds_cache_size option. By default, limiting the MDS cache by inode count is disabled.

In addition, you can specify a cache reservation by using the mds_cache_reservation option for MDS operations. The cache reservation is limited as a percentage of the memory or inode limit and is set to 5% by default. The intent of this parameter is to have the MDS maintain an extra reserve of memory for its cache for new metadata operations to use. As a consequence, the MDS should in general operate below its memory limit because it will recall old state from clients in order to drop unused metadata in its cache.

The mds_cache_reservation option replaces the mds_health_cache_threshold option in all situations, except when MDS nodes sends a health alert to the Ceph Monitors indicating the cache is too large. By default, mds_health_cache_threshold is 150% of the maximum cache size.

Be aware that the cache limit is not a hard limit. Potential bugs in the CephFS client or MDS or misbehaving applications might cause the MDS to exceed its cache size. The mds_health_cache_threshold option configures the storage cluster health warning message, so that operators can investigate why the MDS cannot shrink its cache.

Additional Resources

2.5. Configuring multiple active Metadata Server daemons

Configure multiple active Metadata Server (MDS) daemons to scale metadata performance for large systems.

Important

Do not convert all standby MDS daemons to active ones. A Ceph File System (CephFS)requires at least one standby MDS daemon to remain highly available.

Important

The scrubbing process is not currently supported when multiple active MDS daemons are configured.

Prerequisites

  • Ceph administration capabilities on the MDS node.

Procedure

  1. Set the max_mds parameter to the desired number of active MDS daemons:

    Syntax

    ceph fs set NAME max_mds NUMBER

    Example

    [root@mon ~]# ceph fs set cephfs max_mds 2

    This example increases the number of active MDS daemons to two in the CephFS called cephfs

    Note

    Ceph only increases the actual number of ranks in the CephFS if a spare MDS daemon is available to take the new rank.

  2. Verify the number of active MDS daemons:

    Syntax

    ceph fs status NAME

    Example

    [root@mon ~]# ceph fs status cephfs
    cephfs - 0 clients
    ======
    +------+--------+-------+---------------+-------+-------+
    | Rank | State  |  MDS  |    Activity   |  dns  |  inos |
    +------+--------+-------+---------------+-------+-------+
    |  0   | active | node1 | Reqs:    0 /s |   10  |   12  |
    |  1   | active | node2 | Reqs:    0 /s |   10  |   12  |
    +------+--------+-------+---------------+-------+-------+
    +-----------------+----------+-------+-------+
    |       Pool      |   type   |  used | avail |
    +-----------------+----------+-------+-------+
    | cephfs_metadata | metadata | 4638  | 26.7G |
    |   cephfs_data   |   data   |    0  | 26.7G |
    +-----------------+----------+-------+-------+
    
    +-------------+
    | Standby MDS |
    +-------------+
    |    node3    |
    +-------------+

Additional Resources

2.6. Configuring the number of standby daemons

Each Ceph File System (CephFS) can specify the required number of standby daemons to be considered healthy. This number also includes the standby-replay daemon waiting for a rank failure.

Prerequisites

  • User access to the Ceph Monitor node.

Procedure

  1. Set the expected number of standby daemons for a particular CephFS:

    Syntax

    ceph fs set FS_NAME standby_count_wanted NUMBER

    Note

    Setting the NUMBER to zero disables the daemon health check.

    Example

    [root@mon]# ceph fs set cephfs standby_count_wanted 2

    This example sets the expected standby daemon count to two.

2.7. Configuring the standby-replay Metadata Server

Configure each Ceph File System (CephFS) by adding a standby-replay Metadata Server (MDS) daemon. Doing this reduces failover time if the active MDS becomes unavailable.

This specific standby-replay daemon follows the active MDS’s metadata journal. The standby-replay daemon is only used by the active MDS of the same rank, and is not available to other ranks.

Important

If using standby-replay, then every active MDS must have a standby-replay daemon.

Prerequisites

  • User access to the Ceph Monitor node.

Procedure

  1. Set the standby-replay for a particular CephFS:

    Syntax

    ceph fs set FS_NAME allow_standby_replay 1

    Example

    [root@mon]# ceph fs set cephfs allow_standby_replay 1

    In this example, the Boolean value is 1, which enables the standby-replay daemons to be assigned to the active Ceph MDS daemons.

    Note

    Setting the allow_standby_replay Boolean value back to 0 only prevents new standby-replay daemons from being assigned. To also stop the running daemons, mark them as failed with the ceph mds fail command.

Additional Resources

2.8. Decreasing the number of active Metadata Server daemons

How to decrease the number of active Ceph File System (CephFS) Metadata Server (MDS) daemons.

Prerequisites

  • The rank that you will remove must be active first, meaning that you must have the same number of MDS daemons as specified by the max_mds parameter.

Procedure

  1. Set the same number of MDS daemons as specified by the max_mds parameter:

    Syntax

    ceph fs status NAME

    Example

    [root@mon ~]# ceph fs status cephfs
    cephfs - 0 clients
    
    +------+--------+-------+---------------+-------+-------+
    | Rank | State  |  MDS  |    Activity   |  dns  |  inos |
    +------+--------+-------+---------------+-------+-------+
    |  0   | active | node1 | Reqs:    0 /s |   10  |   12  |
    |  1   | active | node2 | Reqs:    0 /s |   10  |   12  |
    +------+--------+-------+---------------+-------+-------+
    +-----------------+----------+-------+-------+
    |       Pool      |   type   |  used | avail |
    +-----------------+----------+-------+-------+
    | cephfs_metadata | metadata | 4638  | 26.7G |
    |   cephfs_data   |   data   |    0  | 26.7G |
    +-----------------+----------+-------+-------+
    
    +-------------+
    | Standby MDS |
    +-------------+
    |    node3    |
    +-------------+

  2. On a node with administration capabilities, change the max_mds parameter to the desired number of active MDS daemons:

    Syntax

    ceph fs set NAME max_mds NUMBER

    Example

    [root@mon ~]# ceph fs set cephfs max_mds 1

  3. Wait for the storage cluster to stabilize to the new max_mds value by watching the Ceph File System status.
  4. Verify the number of active MDS daemons:

    Syntax

    ceph fs status NAME

    Example

    [root@mon ~]# ceph fs status cephfs
    cephfs - 0 clients
    
    +------+--------+-------+---------------+-------+-------+
    | Rank | State  |  MDS  |    Activity   |  dns  |  inos |
    +------+--------+-------+---------------+-------+-------+
    |  0   | active | node1 | Reqs:    0 /s |   10  |   12  |
    +------+--------+-------+---------------+-------+-------+
    +-----------------+----------+-------+-------+
    |       Pool      |   type   |  used | avail |
    +-----------------+----------+-------+-------+
    | cephfs_metadata | metadata | 4638  | 26.7G |
    |   cephfs_data   |   data   |    0  | 26.7G |
    +-----------------+----------+-------+-------+
    
    +-------------+
    | Standby MDS |
    +-------------+
    |    node3    |
    |    node2    |
    +-------------+

Additional Resources

2.9. Additional Resources

Chapter 3. Deployment of the Ceph File System

As a storage administrator, you can deploy Ceph File Systems (CephFS) in a storage environment and have clients mount those Ceph File Systems to meet the storage needs.

Basically, the deployment workflow is three steps:

  1. Create a Ceph File System on a Ceph Monitor node.
  2. Create a Ceph client user with the appropriate capabilities, and make the client key available on the node where the Ceph File System will be mounted.
  3. Mount CephFS on a dedicated node, using either a kernel client or a File System in User Space (FUSE) client.

3.1. Prerequisites

  • A running, and healthy Red Hat Ceph Storage cluster.
  • Installation and configuration of the Ceph Metadata Server daemon (ceph-mds).

3.2. Layout, quota, snapshot, and network restrictions

These user capabilities can help you restrict access to a Ceph File System (CephFS) based on the needed requirements.

Important

All user capability flags, except rw, must be specified in alphabetical order.

Layouts and Quotas

When using layouts or quotas, clients require the p flag, in addition to rw capabilities. Setting the p flag restricts all the attributes being set by special extended attributes, those with a ceph. prefix. Also, this restricts other means of setting these fields, such as openc operations with layouts.

Example

client.0
    key: AQAz7EVWygILFRAAdIcuJ10opU/JKyfFmxhuaw==
    caps: [mds] allow rwp
    caps: [mon] allow r
    caps: [osd] allow rw tag cephfs data=cephfs_a

client.1
    key: AQAz7EVWygILFRAAdIcuJ11opU/JKyfFmxhuaw==
    caps: [mds] allow rw
    caps: [mon] allow r
    caps: [osd] allow rw tag cephfs data=cephfs_a

In this example, client.0 can modify layouts and quotas on the file system cephfs_a, but client.1 cannot.

Snapshots

When creating or deleting snapshots, clients require the s flag, in addition to rw capabilities. When the capability string also contains the p flag, the s flag must appear after it.

Example

client.0
    key: AQAz7EVWygILFRAAdIcuJ10opU/JKyfFmxhuaw==
    caps: [mds] allow rw, allow rws path=/temp
    caps: [mon] allow r
    caps: [osd] allow rw tag cephfs data=cephfs_a

In this example, client.0 can create or delete snapshots in the temp directory of file system cephfs_a.

Network

Restricting clients connecting from a particular network.

Example

client.0
  key: AQAz7EVWygILFRAAdIcuJ10opU/JKyfFmxhuaw==
  caps: [mds] allow r network 10.0.0.0/8, allow rw path=/bar network 10.0.0.0/8
  caps: [mon] allow r network 10.0.0.0/8
  caps: [osd] allow rw tag cephfs data=cephfs_a network 10.0.0.0/8

The optional network and prefix length is in CIDR notation, for example, 10.3.0.0/16.

Additional Resources

3.3. Creating a Ceph File System

You can create a Ceph File System (CephFS) on a Ceph Monitor node.

Important

By default, you can create only one CephFS per Ceph Storage cluster.

Prerequisites

  • A running, and healthy Red Hat Ceph Storage cluster.
  • Installation and configuration of the Ceph Metadata Server daemon (ceph-mds).
  • Root-level access to a Ceph monitor node.

Procedure

  1. Create two pools, one for storing data and one for storing metadata:

    Syntax

    ceph osd pool create NAME _PG_NUM

    Example

    [root@mon ~]# ceph osd pool create cephfs_data 64
    [root@mon ~]# ceph osd pool create cephfs_metadata 64

    Typically, the metadata pool can start with a conservative number of Placement Groups (PGs) as it will generally have far fewer objects than the data pool. It is possible to increase the number of PGs if needed. Recommended metadata pool sizes range from 64 PGs to 512 PGs. Size the data pool is proportional to the number and sizes of files you expect in the file system.

    Important

    For the metadata pool, consider to use:

    • A higher replication level because any data loss to this pool can make the whole file system inaccessible.
    • Storage with lower latency such as Solid-State Drive (SSD) disks because this directly affects the observed latency of file system operations on clients.
  2. Create the CephFS:

    Syntax

    ceph fs new NAME METADATA_POOL DATA_POOL

    Example

    [root@mon ~]# ceph fs new cephfs cephfs_metadata cephfs_data

  3. Verify that one or more MDSs enter to the active state based on you configuration.

    Syntax

    ceph fs status NAME

    Example

    [root@mon ~]# ceph fs status cephfs
    cephfs - 0 clients
    ======
    +------+--------+-------+---------------+-------+-------+
    | Rank | State  |  MDS  |    Activity   |  dns  |  inos |
    +------+--------+-------+---------------+-------+-------+
    |  0   | active | node1 | Reqs:    0 /s |   10  |   12  |
    +------+--------+-------+---------------+-------+-------+
    +-----------------+----------+-------+-------+
    |       Pool      |   type   |  used | avail |
    +-----------------+----------+-------+-------+
    | cephfs_metadata | metadata | 4638  | 26.7G |
    |   cephfs_data   |   data   |    0  | 26.7G |
    +-----------------+----------+-------+-------+
    
    +-------------+
    | Standby MDS |
    +-------------+
    |    node3    |
    |    node2    |
    +-------------+----

Additional Resources

3.4. Creating Ceph File Systems with erasure coding (Technology Preview)

By default, Ceph uses replicated pools for data pools. You can also add an additional erasure-coded data pool, if needed. Ceph File Systems (CephFS) backed by erasure-coded pools use less overall storage compared to Ceph File Systems backed by replicated pools. While erasure-coded pools use less overall storage, they also use more memory and processor resources than replicated pools.

Important

The Ceph File System using erasure-coded pools is a Technology Preview feature. Technology Preview features are not supported with Red Hat production service level agreements (SLAs), might not be functionally complete, and Red Hat does not recommend to use them for production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process. See the support scope for Red Hat Technology Preview features for more details.

Important

For production environments, Red Hat recommends using a replicated pool as the default data pool.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • A running CephFS environment.
  • Pools using BlueStore OSDs.
  • User-level access to a Ceph Monitor node.

Procedure

  1. Create a replicated metadata pool for CephFS metadata:

    Syntax

    ceph osd pool create METADATA_POOL PG_NUM

    Example

    [root@mon ~]# ceph osd pool create cephfs-metadata 64

    This example creates a pool named cephfs-metadata with 64 placement groups.

  2. Create a default replicated data pool for CephFS:

    Syntax

    ceph osd pool create DATA_POOL PG_NUM

    Example

    [root@mon ~]# ceph osd pool create cephfs-data 64

    This example creates a replicated pool named cephfs-data with 64 placement groups.

  3. Create an erasure-coded data pool for CephFS:

    Syntax

    ceph osd pool create DATA_POOL PG_NUM erasure

    Example

    [root@mon ~]# ceph osd pool create cephfs-data-ec 64 erasure

    This example creates an erasure-coded pool named cephfs-data-ec with 64 placement groups.

  4. Enable overwrites on the erasure-coded pool:

    Syntax

    ceph osd pool set DATA_POOL allow_ec_overwrites true

    Example

    [root@mon ~]# ceph osd pool set cephfs-data-ec allow_ec_overwrites true

    This example enables overwrites on an erasure-coded pool named cephfs-data-ec.

  5. Add the erasure-coded data pool to the CephFS Metadata Server (MDS):

    Syntax

    ceph fs add_data_pool cephfs-ec DATA_POOL

    Example

    [root@mon ~]# ceph fs add_data_pool cephfs-ec cephfs-data-ec

    1. Optionally, verify the data pool was added:

      [root@mon ~]# ceph fs ls
  6. Create the CephFS:

    Syntax

    ceph fs new cephfs METADATA_POOL DATA_POOL

    Example

    [root@mon ~]# ceph fs new cephfs cephfs-metadata cephfs-data

    Important

    Using an erasure-coded pool for the default data pool is not recommended.

  7. Create the CephFS using erasure coding:

    Syntax

    ceph fs new cephfs-ec METADATA_POOL DATA_POOL

    Example

    [root@mon ~]# ceph fs new cephfs-ec cephfs-metadata cephfs-data-ec

  8. Verify that one or more Ceph FS Metadata Servers (MDS) enters the active state:

    Syntax

    ceph fs status FS_EC

    Example

    [root@mon ~]# ceph fs status cephfs-ec
    cephfs-ec - 0 clients
    ======
    +------+--------+-------+---------------+-------+-------+
    | Rank | State  |  MDS  |    Activity   |  dns  |  inos |
    +------+--------+-------+---------------+-------+-------+
    |  0   | active | node1 | Reqs:    0 /s |   10  |   12  |
    +------+--------+-------+---------------+-------+-------+
    +-----------------+----------+-------+-------+
    |       Pool      |   type   |  used | avail |
    +-----------------+----------+-------+-------+
    | cephfs-metadata | metadata | 4638  | 26.7G |
    |  cephfs-data    |   data   |    0  | 26.7G |
    |  cephfs-data-ec |   data   |    0  | 26.7G |
    +-----------------+----------+-------+-------+
    
    +-------------+
    | Standby MDS |
    +-------------+
    |    node3    |
    |    node2    |
    +-------------+

  9. To add a new erasure-coded data pool to an existing file system.

    1. Create an erasure-coded data pool for CephFS:

      Syntax

      ceph osd pool create DATA_POOL PG_NUM erasure

      Example

      [root@mon ~]# ceph osd pool create cephfs-data-ec1 64 erasure

    2. Enable overwrites on the erasure-coded pool:

      Syntax

      ceph osd pool set DATA_POOL allow_ec_overwrites true

      Example

      [root@mon ~]# ceph osd pool set cephfs-data-ec1 allow_ec_overwrites true

    3. Add the erasure-coded data pool to the CephFS Metadata Server (MDS):

      Syntax

      ceph fs add_data_pool cephfs-ec DATA_POOL

      Example

      [root@mon ~]# ceph fs add_data_pool cephfs-ec cephfs-data-ec1

  10. Create the CephFS using erasure coding:

    Syntax

    ceph fs new cephfs-ec METADATA_POOL DATA_POOL

    Example

    [root@mon ~]# ceph fs new cephfs-ec cephfs-metadata cephfs-data-ec1

Additional Resources

3.5. Creating client users for a Ceph File System

Red Hat Ceph Storage uses cephx for authentication, which is enabled by default. To use cephx with the Ceph File System, create a user with the correct authorization capabilities on a Ceph Monitor node and make its key available on the node where the Ceph File System will be mounted.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Installation and configuration of the Ceph Metadata Server daemon (ceph-mds).
  • Root-level access to a Ceph monitor node.
  • Root-level access to a Ceph client node.

Procedure

  1. On a Ceph Monitor node, create a client user:

    Syntax

    ceph fs authorize FILE_SYSTEM_NAME client.CLIENT_NAME /DIRECTORY CAPABILITY [/DIRECTORY CAPABILITY] ...

    • To restrict the client to only writing in the temp directory of filesystem cephfs_a:

      Example

      [root@mon ~]# ceph fs authorize cephfs_a client.1 / r /temp rw
      
      client.1
        key: AQBSdFhcGZFUDRAAcKhG9Cl2HPiDMMRv4DC43A==
        caps: [mds] allow r, allow rw path=/temp
        caps: [mon] allow r
        caps: [osd] allow rw tag cephfs data=cephfs_a

    • To completely restrict the client to the temp directory, remove the root (/) directory:

      Example

      [root@mon ~]# ceph fs authorize cephfs_a client.1 /temp rw

    Note

    Supplying all or asterisk as the file system name grants access to every file system. Typically, it is necessary to quote the asterisk to protect it from the shell.

  2. Verify the created key:

    Syntax

    ceph auth get client.ID

    Example

    [root@mon ~]# ceph auth get client.1

  3. Copy the keyring to the client.

    1. On the Ceph Monitor node, export the keyring to a file:

      Syntax

      ceph auth get client.ID -o ceph.client.ID.keyring

      Example

      [root@mon ~]# ceph auth get client.1 -o ceph.client.1.keyring
      exported keyring for client.1

    2. Copy the client keyring from the Ceph Monitor node to the /etc/ceph/ directory on the client node:

      Syntax

      scp root@MONITOR_NODE_NAME:/root/ceph.client.1.keyring /etc/ceph/

      Replace_MONITOR_NODE_NAME_with the Ceph Monitor node name or IP.

      Example

      [root@client ~]# scp root@mon:/root/ceph.client.1.keyring /etc/ceph/ceph.client.1.keyring

  4. Set the appropriate permissions for the keyring file:

    Syntax

    chmod 644 KEYRING

    Example

    [root@client ~]# chmod 644 /etc/ceph/ceph.client.1.keyring

Additional Resources

  • See the User Management chapter in the Red Hat Ceph Storage Administration Guide for more details.

3.6. Mounting the Ceph File System as a kernel client

You can mount the Ceph File System (CephFS) as a kernel client, either manually or automatically on system boot.

Important

Clients running on other Linux distributions, aside from Red Hat Enterprise Linux, are permitted but not supported. If issues are found in the CephFS Metadata Server or other parts of the storage cluster when using these clients, Red Hat will address them. If the cause is found to be on the client side, then the issue will have to be addressed by the kernel vendor of the Linux distribution.

Prerequisites

  • Root-level access to a Linux-based client node.
  • User-level access to a Ceph Monitor node.
  • An existing Ceph File System.

Procedure

  1. Configure the client node to use the Ceph storage cluster.

    1. Enable the Red Hat Ceph Storage 4 Tools repository:

      Red Hat Enterprise Linux 7

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

      Red Hat Enterprise Linux 8

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

    2. Install the ceph-common package:

      Red Hat Enterprise Linux 7

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

      Red Hat Enterprise Linux 8

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

    3. Copy the Ceph client keyring from the Ceph Monitor node to the client node:

      Syntax

      scp root@MONITOR_NODE_NAME:/etc/ceph/KEYRING_FILE /etc/ceph/

      Replace MONITOR_NODE_NAME with the Ceph Monitor host name or IP address.

      Example

      [root@client ~]# scp root@192.168.0.1:/etc/ceph/ceph.client.1.keyring /etc/ceph/

    4. Copy the Ceph configuration file from a Ceph Monitor node to the client node:

      Syntax

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

      Replace MONITOR_NODE_NAME with the Ceph Monitor host name or IP address.

      Example

      [root@client ~]# scp root@192.168.0.1:/etc/ceph/ceph.conf /etc/ceph/ceph.conf

    5. Set the appropriate permissions for the configuration file:

      [root@client ~]# chmod 644 /etc/ceph/ceph.conf
    6. Choose either automatically or manually mounting.

Manually Mounting

  1. Create a mount directory on the client node:

    Syntax

    mkdir -p MOUNT_POINT

    Example

    [root@client]# mkdir -p /mnt/cephfs

  2. Mount the Ceph File System. To specify multiple Ceph Monitor addresses, separate them with commas in the mount command, specify the mount point, and set the client name:

    Note

    As of Red Hat Ceph Storage 4.1, mount.ceph can read keyring files directly. As such, a secret file is no longer necessary. Just specify the client ID with name=CLIENT_ID, and mount.ceph will find the right keyring file.

    Syntax

    mount -t ceph MONITOR-1_NAME:6789,MONITOR-2_NAME:6789,MONITOR-3_NAME:6789:/ MOUNT_POINT -o name=CLIENT_ID

    Example

    [root@client ~]# mount -t ceph mon1:6789,mon2:6789,mon3:6789:/ /mnt/cephfs -o name=1

    Note

    You can configure a DNS server so that a single host name resolves to multiple IP addresses. Then you can use that single host name with the mount command, instead of supplying a comma-separated list.

    Note

    You can also replace the Monitor host names with the string :/ and mount.ceph will read the Ceph configuration file to determine which Monitors to connect to.

  3. Verify that the file system is successfully mounted:

    Syntax

    stat -f MOUNT_POINT

    Example

    [root@client ~]# stat -f /mnt/cephfs

Automatically Mounting

  1. On the client host, create a new directory for mounting the Ceph File System.

    Syntax

    mkdir -p MOUNT_POINT

    Example

    [root@client ~]# mkdir -p /mnt/cephfs

  2. Edit the /etc/fstab file as follows:

    Syntax

    #DEVICE                 PATH           TYPE     OPTIONS               DUMP  FSCK
    HOST_NAME:_PORT_,     MOUNT_POINT  ceph     name=CLIENT_ID,        0     0
    HOST_NAME:_PORT_,                             ceph.client_mountpoint=/VOL/SUB_VOL_GROUP/SUB_VOL/UID_SUB_VOL,
    HOST_NAME:_PORT_:/                            [ADDITIONAL_OPTIONS]

    The first column sets the Ceph Monitor host names and the port number.

    The second column sets the mount point

    The third column sets the file system type, in this case, ceph, for CephFS.

    The fourth column sets the various options, such as, the user name and the secret file using the name and secretfile options, respectively. You can also set specific volumes, sub-volume groups, and sub-volumes using the ceph.client_mountpoint option.

    Set the _netdev option to ensure that the file system is mounted after the networking subsystem starts to prevent hanging and networking issues. If you do not need access time information, then setting the noatime option can increase performance.

    Set the fifth and sixth columns to zero.

    Example

    #DEVICE         PATH                   TYPE    OPTIONS         DUMP  FSCK
    mon1:6789,      /mnt/cephfs            ceph    name=1,            0     0
    mon2:6789,                                     ceph.client_mountpoint=/my_vol/my_sub_vol_group/my_sub_vol/0,
    mon3:6789:/                                    _netdev,noatime

    The Ceph File System will be mounted on the next system boot.

    Note

    As of Red Hat Ceph Storage 4.1, mount.ceph can read keyring files directly. As such, a secret file is no longer necessary. Just specify the client ID with name=CLIENT_ID, and mount.ceph will find the right keyring file.

    Note

    You can also replace the Monitor host names with the string :/ and mount.ceph will read the Ceph configuration file to determine which Monitors to connect to.

Additional Resources

  • See the mount(8) manual page.
  • See the Ceph user management chapter in the Red Hat Ceph Storage Administration Guide for more details on creating a Ceph user.
  • See the Creating a Ceph File System section of the Red Hat Ceph Storage File System Guide for details.

3.7. Mounting the Ceph File System as a FUSE client

You can mount the Ceph File System (CephFS) as a File System in User Space (FUSE) client, either manually or automatically on system boot.

Prerequisites

  • Root-level access to a Linux-based client node.
  • User-level access to a Ceph Monitor node.
  • An existing Ceph File System.

Procedure

  1. Configure the client node to use the Ceph storage cluster.

    1. Enable the Red Hat Ceph Storage 4 Tools repository:

      Red Hat Enterprise Linux 7

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

      Red Hat Enterprise Linux 8

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

    2. Install the ceph-fuse package:

      Red Hat Enterprise Linux 7

      [root@client ~]# yum install ceph-fuse

      Red Hat Enterprise Linux 8

      [root@client ~]# dnf install ceph-fuse

    3. Copy the Ceph client keyring from the Ceph Monitor node to the client node:

      Syntax

      scp root@MONITOR_NODE_NAME:/etc/ceph/KEYRING_FILE /etc/ceph/

      Replace MONITOR_NODE_NAME with the Ceph Monitor host name or IP address.

      Example

      [root@client ~]# scp root@192.168.0.1:/etc/ceph/ceph.client.1.keyring /etc/ceph/

    4. Copy the Ceph configuration file from a Ceph Monitor node to the client node:

      Syntax

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

      Replace MONITOR_NODE_NAME with the Ceph Monitor host name or IP address.

      Example

      [root@client ~]# scp root@192.168.0.1:/etc/ceph/ceph.conf /etc/ceph/ceph.conf

    5. Set the appropriate permissions for the configuration file:

      [root@client ~]# chmod 644 /etc/ceph/ceph.conf
    6. Choose either automatically or manually mounting.

Manually Mounting

  1. On the client node, create a directory for the mount point:

    Syntax

    mkdir PATH_TO_MOUNT_POINT

    Example

    [root@client ~]# mkdir /mnt/mycephfs

    Note

    If you used the path option with MDS capabilities, then the mount point must be within what is specified by path.

  2. Use the ceph-fuse utility to mount the Ceph File System.

    Syntax

    ceph-fuse -n client.CLIENT_ID MOUNT_POINT

    Example

    [root@client ~]# ceph-fuse -n client.1 /mnt/mycephfs

    Note

    If you do not use the default name and location of the user keyring, that is /etc/ceph/ceph.client.CLIENT_ID.keyring, then use the --keyring option to specify the path to the user keyring, for example:

    Example

    [root@client ~]# ceph-fuse -n client.1 --keyring=/etc/ceph/client.1.keyring /mnt/mycephfs

    Note

    Use the -r option to instruct the client to treat that path as its root:

    Syntax

    ceph-fuse -n client.CLIENT_ID MOUNT_POINT -r PATH

    Example

    [root@client ~]# ceph-fuse -n client.1 /mnt/cephfs -r /home/cephfs

  3. Verify that the file system is successfully mounted:

    Syntax

    stat -f MOUNT_POINT

    Example

    [user@client ~]$ stat -f /mnt/cephfs

Automatically Mounting

  1. On the client node, create a directory for the mount point:

    Syntax

    mkdir PATH_TO_MOUNT_POINT

    Example

    [root@client ~]# mkdir /mnt/mycephfs

    Note

    If you used the path option with MDS capabilities, then the mount point must be within what is specified by path.

  2. Edit the /etc/fstab file as follows:

    Syntax

    #DEVICE                 PATH           TYPE          OPTIONS                  DUMP  FSCK
    HOST_NAME:_PORT_,     MOUNT_POINT  fuse.ceph     ceph.id=CLIENT_ID,        0     0
    HOST_NAME:_PORT_,                                  ceph.client_mountpoint=/VOL/SUB_VOL_GROUP/SUB_VOL/UID_SUB_VOL,
    HOST_NAME:_PORT_:/                                 [ADDITIONAL_OPTIONS]

    The first column sets the Ceph Monitor host names and the port number.

    The second column sets the mount point

    The third column sets the file system type, in this case, fuse.ceph, for CephFS.

    The fourth column sets the various options, such as, the user name and the secret file using the name and secretfile options, respectively. You can also set specific volumes, sub-volume groups, and sub-volumes using the ceph.client_mountpoint option. Set the _netdev option to ensure that the file system is mounted after the networking subsystem starts to prevent hanging and networking issues. If you do not need access time information, then setting the noatime option can increase performance.

    Set the fifth and sixth columns to zero.

    Example

    #DEVICE         PATH              TYPE         OPTIONS         DUMP  FSCK
    mon1:6789,      /mnt/cephfs       fuse.ceph    ceph.id=1,         0     0
    mon2:6789,                                     ceph.client_mountpoint=/my_vol/my_sub_vol_group/my_sub_vol/0,
    mon3:6789:/                                    _netdev,defaults

    The Ceph File System will be mounted on the next system boot.

Additional Resources

  • The ceph-fuse(8) manual page.
  • See the Ceph user management chapter in the Red Hat Ceph Storage Administration Guide for more details on creating a Ceph user.
  • See the Creating a Ceph File System section of the Red Hat Ceph Storage File System Guide for details.

3.8. Additional Resources

Chapter 4. Ceph File System administration

As a storage administrator, you can perform common Ceph File System (CephFS) administrative tasks, such as:

4.1. Prerequisites

  • A running, and healthy Red Hat Ceph Storage cluster.
  • Installation and configuration of the Ceph Metadata Server daemons (ceph-mds).
  • Create and mount the Ceph File System.

4.2. Unmounting Ceph File Systems mounted as kernel clients

How to unmount a Ceph File System that is mounted as a kernel client.

Prerequisites

  • Root-level access to the node doing the mounting.

Procedure

  1. To unmount a Ceph File System mounted as a kernel client:

    Syntax

    umount MOUNT_POINT

    Example

    [root@client ~]# umount /mnt/cephfs

Additional Resources

  • The umount(8) manual page

4.3. Unmounting Ceph File Systems mounted as FUSE clients

Unmounting a Ceph File System that is mounted as a File System in User Space (FUSE) client.

Prerequisites

  • Root-level access to the FUSE client node.

Procedure

  1. To unmount a Ceph File System mounted in FUSE:

    Syntax

    fusermount -u MOUNT_POINT

    Example

    [root@client ~]# fusermount -u /mnt/cephfs

Additional Resources

  • The ceph-fuse(8) manual page

4.4. Mapping directory trees to Metadata Server daemon ranks

To map a directory and its subdirectories to a particular active Metadata Server (MDS) rank so that its metadata is only managed by the MDS daemon holding that rank. This approach enables you to evenly spread application load or limit impact of users' metadata requests to the entire storage cluster.

Important

An internal balancer already dynamically spreads the application load. Therefore, only map directory trees to ranks for certain carefully chosen applications.

In addition, when a directory is mapped to a rank, the balancer cannot split it. Consequently, a large number of operations within the mapped directory can overload the rank and the MDS daemon that manages it.

Prerequisites

  • At least two active MDS daemons.
  • User access to the CephFS client node.
  • Verify that the attr package is installed on the CephFS client node with a mounted Ceph File System.

Procedure

  1. Add the p flag to the Ceph user’s capabilities:

    Syntax

    ceph fs authorize FILE_SYSTEM_NAME client.CLIENT_NAME /DIRECTORY CAPABILITY [/DIRECTORY CAPABILITY] ...

    Example

    [user@client ~]$ ceph fs authorize cephfs_a client.1 /temp rwp
    
    client.1
      key: AQBSdFhcGZFUDRAAcKhG9Cl2HPiDMMRv4DC43A==
      caps: [mds] allow r, allow rwp path=/temp
      caps: [mon] allow r
      caps: [osd] allow rw tag cephfs data=cephfs_a

  2. Set the ceph.dir.pin extended attribute on a directory:

    Syntax

    setfattr -n ceph.dir.pin -v RANK DIRECTORY

    Example

    [user@client ~]$ setfattr -n ceph.dir.pin -v 2 /temp

    This example assigns the /temp directory and all of its subdirectories to rank 2.

Additional Resources

4.5. Disassociating directory trees from Metadata Server daemon ranks

Disassociate a directory from a particular active Metadata Server (MDS) rank.

Prerequisites

  • User access to the Ceph File System (CephFS) client node.
  • Ensure that the attr package is installed on the client node with a mounted CephFS.

Procedure

  1. Set the ceph.dir.pin extended attribute to -1 on a directory:

    Syntax

    setfattr -n ceph.dir.pin -v -1 DIRECTORY

    Example

    [user@client ~]$ serfattr -n ceph.dir.pin -v -1 /home/ceph-user

    Note

    Any separately mapped subdirectories of /home/ceph-user/ are not affected.

Additional Resources

4.6. Adding data pools

The Ceph File System (CephFS) supports adding more than one pool to be used for storing data. This can be useful for:

  • Storing log data on reduced redundancy pools
  • Storing user home directories on an SSD or NVMe pool
  • Basic data segregation.

Before using another data pool in the Ceph File System, you must add it as described in this section.

By default, for storing file data, CephFS uses the initial data pool that was specified during its creation. To use a secondary data pool, you must also configure a part of the file system hierarchy to store file data in that pool or optionally within a namespace of that pool, using file and directory layouts.

Prerequisites

  • Root-level access to the Ceph Monitor node.

Procedure

  1. Create a new data pool:

    Syntax

    ceph osd pool create POOL_NAME PG_NUMBER

    Replace:

    • POOL_NAME with the name of the pool.
    • PG_NUMBER with the number of placement groups (PGs).

    Example

    [root@mon ~]# ceph osd pool create cephfs_data_ssd 64
    pool 'cephfs_data_ssd' created

  2. Add the newly created pool under the control of the Metadata Servers:

    Syntax

    ceph fs add_data_pool FS_NAME POOL_NAME

    Replace:

    • FS_NAME with the name of the file system.
    • POOL_NAME with the name of the pool.

    Example:

    [root@mon ~]# ceph fs add_data_pool cephfs cephfs_data_ssd
    added data pool 6 to fsmap

  3. Verify that the pool was successfully added:

    Example

    [root@mon ~]# ceph fs ls
    name: cephfs, metadata pool: cephfs_metadata, data pools: [cephfs_data cephfs_data_ssd]

  4. If you use the cephx authentication, make sure that clients can access the new pool.

Additional Resources

4.7. Working with Ceph File System quotas

As a storage administrator, you can view, set, and remove quotas on any directory in the file system. You can place quota restrictions on the number of bytes or the number of files within the directory.

4.7.1. Prerequisites

  • Make sure that the attr package is installed.

4.7.2. Ceph File System quotas

The Ceph File System (CephFS) quotas allow you to restrict the number of bytes or the number of files stored in the directory structure.

Limitations

  • CephFS quotas rely on the cooperation of the client mounting the file system to stop writing data when it reaches the configured limit. However, quotas alone cannot prevent an adversarial, untrusted client from filling the file system.
  • Once processes that write data to the file system reach the configured limit, a short period of time elapses between when the amount of data reaches the quota limit, and when the processes stop writing data. The time period generally measures in the tenths of seconds. However, processes continue to write data during that time. The amount of additional data that the processes write depends on the amount of time elapsed before they stop.
  • Previously, quotas were only supported with the userspace FUSE client. With Linux kernel version 4.17 or newer, the CephFS kernel client supports quotas against Ceph mimic or newer clusters. Those version requirements are met by Red Hat Enterprise Linux 8 and Red Hat Ceph Storage 4, respectively. The userspace FUSE client can be used on older and newer OS and cluster versions. The FUSE client is provided by the ceph-fuse package.
  • When using path-based access restrictions, be sure to configure the quota on the directory to which the client is restricted, or to a directory nested beneath it. If the client has restricted access to a specific path based on the MDS capability, and the quota is configured on an ancestor directory that the client cannot access, the client will not enforce the quota. For example, if the client cannot access the /home/ directory and the quota is configured on /home/, the client cannot enforce that quota on the directory /home/user/.
  • Snapshot file data that has been deleted or changed does not count towards the quota.

4.7.3. Viewing quotas

Use the getfattr command and the ceph.quota extended attributes to view the quota settings for a directory.

Note

If the attributes appear on a directory inode, then that directory has a configured quota. If the attributes do not appear on the inode, then the directory does not have a quota set, although its parent directory might have a quota configured. If the value of the extended attribute is 0, the quota is not set.

Prerequisites

  • Make sure that the attr package is installed.

Procedure

  1. To view CephFS quotas.

    1. Using a byte-limit quota:

      Syntax

      getfattr -n ceph.quota.max_bytes DIRECTORY

      Example

      [root@fs ~]# getfattr -n ceph.quota.max_bytes /cephfs/

    2. Using a file-limit quota:

      Syntax

      getfattr -n ceph.quota.max_files DIRECTORY

      Example

      [root@fs ~]# getfattr -n ceph.quota.max_files /cephfs/

Additional Resources

  • See the getfattr(1) manual page for more information.

4.7.4. Setting quotas

This section describes how to use the setfattr command and the ceph.quota extended attributes to set the quota for a directory.

Prerequisites

  • Make sure that the attr package is installed.

Procedure

  1. To set CephFS quotas.

    1. Using a byte-limit quota:

      Syntax

      setfattr -n ceph.quota.max_bytes -v 100000000 /some/dir

      Example

      [root@fs ~]# setfattr -n ceph.quota.max_bytes -v 100000000 /cephfs/

      In this example, 100000000 bytes equals 100 MB.

    2. Using a file-limit quota:

      Syntax

      setfattr -n ceph.quota.max_files -v 10000 /some/dir

      Example

      [root@fs ~]# setfattr -n ceph.quota.max_files -v 10000 /cephfs/

      In this example, 10000 equals 10,000 files.

Additional Resources

  • See the setfattr(1) manual page for more information.

4.7.5. Removing quotas

This section describes how to use the setfattr command and the ceph.quota extended attributes to remove a quota from a directory.

Prerequisites

  • Make sure that the attr package is installed.

Procedure

  1. To remove CephFS quotas.

    1. Using a byte-limit quota:

      Syntax

      setfattr -n ceph.quota.max_bytes -v 0 DIRECTORY

      Example

      [root@fs ~]# setfattr -n ceph.quota.max_bytes -v 0 /cephfs/

    2. Using a file-limit quota:

      Syntax

      setfattr -n ceph.quota.max_files -v 0 DIRECTORY

      Example

      [root@fs ~]# setfattr -n ceph.quota.max_files -v 0 /cephfs/

Additional Resources

  • See the setfattr(1) manual page for more information.

4.7.6. Additional Resources

  • See the getfattr(1) manual page for more information.
  • See the setfattr(1) manual page for more information.

4.8. Working with File and Directory Layouts

As a storage administrator, you can control how file or directory data is mapped to objects.

This section describes how to:

4.8.1. Prerequisites

  • The installation of the attr package.

4.8.2. Overview of file and directory layouts

This section explains what file and directory layouts are in the context for the Ceph File System.

A layout of a file or directory controls how its content is mapped to Ceph RADOS objects. The directory layouts serves primarily for setting an inherited layout for new files in that directory.

To view and set a file or directory layout, use virtual extended attributes or extended file attributes (xattrs). The name of the layout attributes depends on whether a file is a regular file or a directory:

  • Regular files layout attributes are called ceph.file.layout.
  • Directories layout attributes are called ceph.dir.layout.

The File and Directory Layout Fields table lists available layout fields that you can set on files and directories.

Layouts Inheritance

Files inherit the layout of their parent directory when you create them. However, subsequent changes to the parent directory layout do not affect children. If a directory does not have any layouts set, files inherit the layout from the closest directory with layout in the directory structure.

Additional Resources

4.8.3. Setting file and directory layout fields

Use the setfattr command to set layout fields on a file or directory.

Important

When you modify the layout fields of a file, the file must be empty, otherwise an error occurs.

Prerequisites

  • Root-level access to the node.

Procedure

  1. To modify layout fields on a file or directory:

    Syntax

    setfattr -n ceph.TYPE.layout.FIELD -v VALUE PATH

    Replace:

    • TYPE with file or dir.
    • FIELD with the name of the field.
    • VALUE with the new value of the field.
    • PATH with the path to the file or directory.

    Example

    [root@fs ~]# setfattr -n ceph.file.layout.stripe_unit -v 1048576 test

Additional Resources

4.8.4. Viewing file and directory layout fields

To use the getfattr command to view layout fields on a file or directory.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to all nodes in the storage cluster.

Procedure

  1. To view layout fields on a file or directory as a single string:

    Syntax

    getfattr -n ceph.TYPE.layout PATH

    Replace
    • PATH with the path to the file or directory.
    • TYPE with file or dir.

    Example

    [root@mon ~] getfattr -n ceph.dir.layout /home/test
    ceph.dir.layout="stripe_unit=4194304 stripe_count=2 object_size=4194304 pool=cephfs_data"

Note

A directory does not have an explicit layout until you set it. Consequently, attempting to view the layout without first setting it fails because there are no changes to display.

Additional Resources

4.8.5. Viewing individual layout fields

Use the getfattr command to view individual layout fields for a file or directory.

Prerequisites

  • A running Red Hat Ceph Storage cluster.
  • Root-level access to all nodes in the storage cluster.

Procedure

  1. To view individual layout fields on a file or directory:

    Syntax

    getfattr -n ceph.TYPE.layout.FIELD _PATH

    Replace
    • TYPE with file or dir.
    • FIELD with the name of the field.
    • PATH with the path to the file or directory.

    Example

    [root@mon ~] getfattr -n ceph.file.layout.pool test
    ceph.file.layout.pool="cephfs_data"

    Note

    Pools in the pool field are indicated by name. However, newly created pools can be indicated by ID.

Additional Resources

4.8.6. Removing directory layouts

Use the setfattr command to remove layouts from a directory.

Note

When you set a file layout, you cannot change or remove it.

Prerequisites

  • A directory with a layout.

Procedure

  1. To remove a layout from a directory:

    Syntax

    setfattr -x ceph.dir.layout DIRECTORY_PATH

    Example

    [user@client ~]$ setfattr -x ceph.dir.layout /home/cephfs

  2. To remove the pool_namespace field:

    Syntax

    setfattr -x ceph.dir.layout.pool_namespace DIRECTORY_PATH

    Example

    [user@client ~]$ setfattr -x ceph.dir.layout.pool_namespace /home/cephfs

    Note

    The pool_namespace field is the only field you can remove separately.

Additional Resources

  • The setfattr(1) manual page

4.9. Taking down a Ceph File System cluster

You can take down Ceph File System (CephFS) cluster by simply setting the down flag true. Doing this gracefully shuts down the Metadata Server (MDS) daemons by flushing journals to the metadata pool and all client I/O is stopped.

You can also take the CephFS cluster down quickly for testing the deletion of a file system and bring the Metadata Server (MDS) daemons down, for example, practicing a disaster recovery scenario. Doing this sets the jointable flag to prevent the MDS standby daemons from activating the file system.

Prerequisites

  • User access to the Ceph Monitor node.

Procedure

  1. To mark the CephFS cluster down:

    Syntax

    ceph fs set FS_NAME down true

    Exmaple

    [root@mon]# ceph fs set cephfs down true

    1. To bring the CephFS cluster back up:

      Syntax

      ceph fs set FS_NAME down false

      Exmaple

      [root@mon]# ceph fs set cephfs down false

    or

  1. To quickly take down a CephFS cluster:

    Syntax

    ceph fs fail FS_NAME

    Exmaple

    [root@mon]# ceph fs fail cephfs

4.10. Removing a Ceph File System

You can remove a Ceph File System (CephFS). Before doing so, consider backing up all the data and verifying that all clients have unmounted the file system locally.

Warning

This operation is destructive and will make the data stored on the Ceph File System permanently inaccessible.

Prerequisites

  • Back up your data.
  • Root-level access to a Ceph Monitor node.

Procedure

  1. Display the Ceph File System status to determine the MDS ranks. In a later step you will stop the CephFS by referencing the MDS ranks.

    Syntax

    ceph fs status

    Example

    [root@mon ~]# ceph fs status
    cephfs - 0 clients
    ======
    +------+--------+----------------+---------------+-------+-------+
    | Rank | State  |      MDS       |    Activity   |  dns  |  inos |
    +------+--------+----------------+---------------+-------+-------+
    |  0   | active | cluster1-node6 | Reqs:    0 /s |   10  |   13  |
    +------+--------+----------------+---------------+-------+-------+
    +-----------------+----------+-------+-------+
    |       Pool      |   type   |  used | avail |
    +-----------------+----------+-------+-------+
    | cephfs_metadata | metadata | 2688k | 15.0G |
    |   cephfs_data   |   data   |    0  | 15.0G |
    +-----------------+----------+-------+-------+
    +----------------+
    |  Standby MDS   |
    +----------------+
    | cluster1-node5 |
    +----------------+

    In the example above, the rank is 0.

  2. Mark the Ceph File System as down:

    Syntax

    ceph fs set FS_NAME down true

    Replace FS_NAME with the name of the Ceph File System you want to remove.

    Example

    [root@mon]# ceph fs set cephfs down true
    marked down

  3. Display the status of the Ceph File System to determine it has stopped:

    Syntax

    ceph fs status

    Example

    [root@mon ~]# ceph fs status
    cephfs - 0 clients
    ======
    +------+----------+----------------+----------+-------+-------+
    | Rank |  State   |      MDS       | Activity |  dns  |  inos |
    +------+----------+----------------+----------+-------+-------+
    |  0   | stopping | cluster1-node6 |          |   10  |   12  |
    +------+----------+----------------+----------+-------+-------+
    +-----------------+----------+-------+-------+
    |       Pool      |   type   |  used | avail |
    +-----------------+----------+-------+-------+
    | cephfs_metadata | metadata | 2688k | 15.0G |
    |   cephfs_data   |   data   |    0  | 15.0G |
    +-----------------+----------+-------+-------+
    +----------------+
    |  Standby MDS   |
    +----------------+
    | cluster1-node5 |
    +----------------+

    After some time, the MDS is no longer listed:

    Example

    [root@mon ~]# ceph fs status
    cephfs - 0 clients
    ======
    +------+-------+-----+----------+-----+------+
    | Rank | State | MDS | Activity | dns | inos |
    +------+-------+-----+----------+-----+------+
    +------+-------+-----+----------+-----+------+
    +-----------------+----------+-------+-------+
    |       Pool      |   type   |  used | avail |
    +-----------------+----------+-------+-------+
    | cephfs_metadata | metadata | 2688k | 15.0G |
    |   cephfs_data   |   data   |    0  | 15.0G |
    +-----------------+----------+-------+-------+
    +----------------+
    |  Standby MDS   |
    +----------------+
    | cluster1-node5 |
    +----------------+

  4. Fail all MDS ranks shown in the status of step one:

    Syntax

    ceph mds fail RANK

    Replace RANK with the rank of the MDS daemons to fail.

    Example

    [root@mon]# ceph mds fail 0

  5. Remove the Ceph File System:

    Syntax

    ceph fs rm FS_NAME --yes-i-really-mean-it

    Replace FS_NAME with the name of the Ceph File System you want to remove.

    Example

    [root@mon]# ceph fs rm cephfs --yes-i-really-mean-it

  6. Verify that the file system has been successfully removed:

    Syntax

    ceph fs ls

    Example

    [root@mon ~]# ceph fs ls
    No filesystems enabled

  7. Optional. Remove the data and metadata pools associated with the removed file system.

    1. Delete the CephFS metadata pool:

      Syntax

      ceph osd pool delete CEPH_METADATA_POOL CEPH_METADATA_POOL --yes-i-really-really-mean-it

      Replace CEPH_METADATA_POOL with the pool CephFS used for metadata storage. You must include it twice.

      Example

      [root@mon ~]# ceph osd pool delete cephfs_metadata cephfs_metadata --yes-i-really-really-mean-it
      pool 'cephfs_metadata' removed

    2. Delete the CephFS data pool:

      Syntax

      ceph osd pool delete CEPH_DATA_POOL CEPH_DATA_POOL --yes-i-really-really-mean-it

      Replace CEPH_DATA_POOL with the pool CephFS used for data storage. You must include it twice.

      Example

      [root@mon ~]# ceph osd pool delete cephfs_data cephfs_data --yes-i-really-really-mean-it
      pool 'cephfs_data' removed

Additional Resources

  • See the Delete a pool section in the Red Hat Ceph Storage Storage Strategies Guide.

4.11. Setting a minimum client version

You can set a minimum version of Ceph that a third-party client must be running to connect to a Red Hat Ceph Storage Ceph File System (CephFS). Set the min_compat_client parameter to prevent older clients from mounting the file system. CephFS will also automatically evict currently connected clients that use an older version than the version set with min_compat_client.

The rationale for this setting is to prevent older clients which might include bugs or have incomplete feature compatibility from connecting to the cluster and disrupting other clients. For example, some older versions of CephFS clients might not release capabilities properly and cause other client requests to be handled slowly.

The values of min_compat_client are based on the upstream Ceph versions. Red Hat recommends that the third-party clients use the same major upstream version as the Red Hat Ceph Storage cluster is based on. See the following table to see the upstream versions and corresponding Red Hat Ceph Storage versions.

Table 4.1. min_compat_client values

ValueUpstream Ceph versionRed Hat Ceph Storage version

luminous

12.2

Red Hat Ceph Storage 3

mimic

13.2

not applicable

nautilus

14.2

Red Hat Ceph Storage 4

Important

If you use Red Hat Enterprise Linux 7, do not set min_compat_client to a later version than luminous because Red Hat Enterprise Linux 7 is considered a luminous client and if you use a later version, CephFS does not allow it to access the mount point.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed

Procedure

  1. Set the minimum client version:

    ceph fs set name min_compat_client release

    Replace name with the name of the Ceph File System and release with the minimum client version. For example to restrict clients to use the nautilus upstream version at minimum on the cephfs Ceph File System:

    $ ceph fs set cephfs min_compat_client nautilus

    See Table 4.1, “min_compat_client values” for the full list of available values and how they correspond with Red Hat Ceph Storage versions.

4.12. Using the ceph mds fail command

Use the ceph mds fail command to:

  • Mark an MDS daemon as failed. If the daemon was active and a suitable standby daemon was available, and if the standby daemon was active after disabling the standby-replay configuration, using this command forces a failover to the standby daemon. By disabling the standby-replay daemon, this prevents new standby-replay daemons from being assigned.
  • Restart a running MDS daemon. If the daemon was active and a suitable standby daemon was available, the "failed" daemon becomes a standby daemon.

Prerequisites

  • Installation and configuration of the Ceph MDS daemons.

Procedure

  1. To fail a daemon:

    Syntax

    ceph mds fail MDS_NAME

    Where MDS_NAME is the name of the standby-replay MDS node.

    Example

    [root@mds ~]# ceph mds fail example01

    Note

    You can find the Ceph MDS name from the ceph fs status command.

Additional Resources

4.13. Ceph File System client evictions

When a Ceph File System (CephFS) client is unresponsive or misbehaving, it might be necessary to forcibly terminate, or evict it from accessing the CephFS. Evicting a CephFS client prevents it from communicating further with Metadata Server (MDS) daemons and Ceph OSD daemons. If a CephFS client is buffering I/O to the CephFS at the time of eviction, then any un-flushed data will be lost. The CephFS client eviction process applies to all client types: FUSE mounts, kernel mounts, NFS gateways, and any process using libcephfs API library.

You can evict CephFS clients automatically, if they fail to communicate promptly with the MDS daemon, or manually.

Automatically Evictions

These scenarios cause an automatic CephFS client eviction:

  • If a CephFS client has not communicated with the active MDS daemon for over the default 300 seconds, or as set by the session_autoclose option.
  • If the mds_cap_revoke_eviction_timeout option is set, and a CephFS client has not responded to the cap revoke messages for over the set amount of seconds. The mds_cap_revoke_eviction_timeout option is disabled by default.
  • During MDS startup or failover, the MDS daemon goes through a reconnect phase waiting for all the CephFS clients to connect to the new MDS daemon. If any CephFS clients fails to reconnect within the default time window of 45 seconds, or as set by the mds_reconnect_timeout option.

Additional Resources

4.14. Blacklist Ceph File System clients

Ceph File System client blacklisting is enabled by default. When you send an eviction command to a single Metadata Server (MDS) daemon, it propagates the blacklist to the other MDS daemons. This is to prevent the CephFS client from accessing any data objects, so it is necessary to update the other CephFS clients, and MDS daemons with the latest Ceph OSD map, which includes the blacklisted client entries.

An internal “osdmap epoch barrier” mechanism is used when updating the Ceph OSD map. The purpose of the barrier is to verify the CephFS clients receiving the capabilities have a sufficiently recent Ceph OSD map, before any capabilities are assigned that might allow access to the same RADOS objects, as to not race with cancelled operations, such as, from ENOSPC or blacklisted clients from evictions.

If you are experiencing frequent CephFS client evictions due to slow nodes or an unreliable network, and you cannot fix the underlying issue, then you can ask the MDS to be less strict. It is possible to respond to slow CephFS clients by simply dropping their MDS sessions, but permit the CephFS client to re-open sessions and to continue talking to Ceph OSDs. By setting the mds_session_blacklist_on_timeout and mds_session_blacklist_on_evict options to false enables this mode.

Note

When blacklisting is disabled, the evicted CephFS client has only an effect on the MDS daemon you send the command to. On a system with multiple active MDS daemons, you would need to send an eviction command to each active daemon.

4.15. Manually evicting a Ceph File System client

You might want to manually evict a Ceph File System (CephFS) client, if the client is misbehaving and you do not have access to the client node, or if a client dies, and you do not want to wait for the client session to time out.

Prerequisites

  • User access to the Ceph Monitor node.

Procedure

  1. Review the client list:

    Syntax

    ceph tell DAEMON_NAME client ls

    Exmaple

    [root@mon]# ceph tell mds.0 client ls
    [
        {
            "id": 4305,
            "num_leases": 0,
            "num_caps": 3,
            "state": "open",
            "replay_requests": 0,
            "completed_requests": 0,
            "reconnecting": false,
            "inst": "client.4305 172.21.9.34:0/422650892",
            "client_metadata": {
                "ceph_sha1": "ae81e49d369875ac8b569ff3e3c456a31b8f3af5",
                "ceph_version": "ceph version 12.0.0-1934-gae81e49 (ae81e49d369875ac8b569ff3e3c456a31b8f3af5)",
                "entity_id": "0",
                "hostname": "senta04",
                "mount_point": "/tmp/tmpcMpF1b/mnt.0",
                "pid": "29377",
                "root": "/"
            }
        }
    ]

  2. Evict the specified CephFS client:

    Syntax

    ceph tell DAEMON_NAME client evict id=ID_NUMBER

    Exmaple

    [root@mon]# ceph tell mds.0 client evict id=4305

4.16. Removing a Ceph File System client from the blacklist

In some situations, it can be useful to allow a previous blacklisted Ceph File System (CephFS) client to reconnect to the storage cluster.

Important

Removing a CephFS client from the blacklist puts data integrity at risk, and does not guarantee a fully healthy, and functional CephFS client as a result. The best way to get a fully healthy CephFS client back after an eviction, is to unmount the CephFS client and do a fresh mount. If other CephFS clients are accessing files that the blacklisted CephFS client was doing buffered I/O to can result in data corruption.

Prerequisites

  • User access to the Ceph Monitor node.

Procedure

  1. Review the blacklist:

    Exmaple

    [root@mon]# ceph osd blacklist ls
    listed 1 entries
    127.0.0.1:0/3710147553 2020-03-19 11:32:24.716146

  2. Remove the CephFS client from the blacklist:

    Syntax

    ceph osd blacklist rm CLIENT_NAME_OR_IP_ADDR

    Exmaple

    [root@mon]# ceph osd blacklist rm 127.0.0.1:0/3710147553
    un-blacklisting 127.0.0.1:0/3710147553

  3. Optionally, to have FUSE-based CephFS clients trying automatically to reconnect when removing them from the blacklist. On the FUSE client, set the following option to true:

    client_reconnect_stale = true

4.17. Additional Resources

Chapter 5. Management of Ceph File System volumes, sub-volumes, and sub-volume groups

As a storage administrator, you can use Red Hat’s Ceph Container Storage Interface (CSI) to manage Ceph File System (CephFS) exports. This also allows you to use other services, such as OpenStack’s file system service (Manila) by having a common command-line interface to interact with. The volumes module for the Ceph Manager daemon (ceph-mgr) implements the ability to export Ceph File Systems (CephFS).

The Ceph Manager volumes module implements the following file system export abstractions:

  • CephFS volumes
  • CephFS subvolume groups
  • CephFS subvolumes

This chapter describes how to work with:

5.1. Ceph File System volumes

As a storage administrator, you can create, list, and remove Ceph File System (CephFS) volumes. CephFS volumes are an abstraction for Ceph File Systems.

This section describes how to:

5.1.1. Creating a file system volume

Ceph Manager’s orchestrator module creates a Meta Data Server (MDS) for the Ceph File System (CephFS). This section describes how to create CephFS volume.

Note

This creates the Ceph File System, along with the data and metadata pools.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.

Procedure

  1. Create a CephFS volume:

    Syntax

    ceph fs volume create VOLUME_NAME

    Example

    [root@mon ~]# ceph fs volume create cephfs

5.1.2. Listing file system volume

This section describes the step to list the Ceph File system (CephFS) volumes.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • A CephFS volume.

Procedure

  1. List the CephFS volume:

    Example

    [root@mon ~]# ceph fs volume ls

5.1.3. Removing a file system volume

Ceph Manager’s orchestrator module removes the Meta Data Server (MDS) for the Ceph File System (CephFS). This section shows how to remove the Ceph File system (CephFS) volume.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • A CephFS volume.

Procedure

  1. Remove the CephFS volume:

    Syntax

    ceph fs volume rm VOLUME_NAME [--yes-i-really-mean-it]

    Example

    [root@mon ~]# ceph fs volume rm cephfs --yes-i-really-mean-it

5.2. Ceph File System subvolumes

As a storage administrator, you can create, list, fetch absolute path, fetch metadata, and remove Ceph File System (CephFS) subvolumes. Additionally, you can also create, list and remove snapshots of these subvolumes. CephFS subvolumes are an abstraction for independent Ceph File Systems directory trees.

This section describes how to:

5.2.1. Creating a file system subvolume

This section describes how to create Ceph File system (CephFS) subvolume.

Note

When creating a subvolume you can specify its subvolume group, data pool layout, uid, gid, file mode in octal numerals, and size in bytes. The subvolume can be created in a separate RADOS namespace by specifying`--namespace-isolated` option. By default a subvolume is created within the default subvolume group, and with an octal file mode ‘755’, uid of its subvolume group, gid of its subvolume group, data pool layout of its parent directory and no size limit.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.

Procedure

  1. Create a CephFS subvolume:

    Syntax

    ceph fs subvolume create VOLUME_NAME SUBVOLUME_NAME [--size SIZE_IN_BYTES --group_name SUBVOLUME_GROUP_NAME --pool_layout DATA_POOL_NAME --uid _UID --gid GID --mode OCTAL_MODE] [--namespace-isolated]

    Example

    [root@mon ~]# ceph fs subvolume create cephfs sub0 --group_name subgroup0 --namespace-isolated

    The command succeeds even if the subvolume already exists.

5.2.2. Listing file system subvolume

This section describes the step to list the Ceph File system (CephFS) subvolume.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • A CephFS subvolume.

Procedure

  1. List the CephFS subvolume:

    Syntax

    ceph fs subvolume ls VOLUME_NAME [--group_name SUBVOLUME_GROUP_NAME]

    Example

    [root@mon ~]# ceph fs subvolume ls cephfs --group_name subgroup0

5.2.3. Resizing a file system subvolume

This section describes the step to resize the Ceph File system (CephFS) subvolume.

Note

The ceph fs subvolume resize command resizes the subvolume quota using the size specified by new_size. The --no_shrink flag prevents the subvolume to shrink below the current used size of the subvolume. The subvolume can be resized to an infinite size by passing inf or infinite as the new_size.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • A CephFS subvolume.

Procedure

  1. Resize a CephFS subvolume:

    Syntax

    ceph fs subvolume resize VOLUME_NAME SUBVOLUME_NAME_ NEW_SIZE [--group_name SUBVOLUME_GROUP_NAME] [--no_shrink]

    Example

    [root@mon ~]# ceph fs subvolume resize cephfs sub0 1024000000 --group_name subgroup0 --no_shrink

5.2.4. Fetching absolute path of a file system subvolume

This section shows how to fetch the absolute path of a Ceph File system (CephFS) subvolume.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • A CephFS subvolume.

Procedure

  1. Fetch the absolute path of the CephFS subvolume:

    Syntax

    ceph fs subvolume getpath VOLUME_NAME SUBVOLUME_NAME [--group_name SUBVOLUME_GROUP_NAME]

    Example

    [root@mon ~]# ceph fs subvolume getpath cephfs sub0 --group_name subgroup0

5.2.5. Fetching metadata of a file system subvolume

This section shows how to fetch metadata of a Ceph File system (CephFS) subvolume.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • A CephFS subvolume.

Procedure

  1. Fetch the metadata of a CephFS subvolume:

    Syntax

    ceph fs subvolume info VOLUME_NAME SUBVOLUME_NAME [--group_name SUBVOLUME_GROUP_NAME]

    Example

    [root@mon ~]# ceph fs subvolume info cephfs sub0 --group_name subgroup0

    Example output

    {
        "atime": "2020-09-08 09:27:15",
        "bytes_pcent": "undefined",
        "bytes_quota": "infinite",
        "bytes_used": 0,
        "created_at": "2020-09-08 09:27:15",
        "ctime": "2020-09-08 09:27:15",
        "data_pool": "cephfs_data",
        "features": [
            "snapshot-clone",
            "snapshot-autoprotect",
            "snapshot-retention"
        ],
        "gid": 0,
        "mode": 16877,
        "mon_addrs": [
            "10.8.128.22:6789",
            "10.8.128.23:6789",
            "10.8.128.24:6789"
        ],
        "mtime": "2020-09-08 09:27:15",
        "path": "/volumes/subgroup0/sub0/6d01a68a-e981-4ebe-84ca-96b660879173",
        "pool_namespace": "",
        "state": "complete",
        "type": "subvolume",
        "uid": 0
    }

The output format is a json and contains the following fields:

  • atime: access time of subvolume path in the format "YYYY-MM-DD HH:MM:SS".
  • mtime: modification time of subvolume path in the format "YYYY-MM-DD HH:MM:SS".
  • ctime: change time of subvolume path in the format "YYYY-MM-DD HH:MM:SS".
  • uid: uid of subvolume path.
  • gid: gid of subvolume path.
  • mode: mode of subvolume path.
  • mon_addrs: list of monitor addresses.
  • bytes_pcent: quota used in percentage if quota is set, else displays "undefined".
  • bytes_quota: quota size in bytes if quota is set, else displays "infinite".
  • bytes_used: current used size of the subvolume in bytes.
  • created_at: time of creation of subvolume in the format "YYYY-MM-DD HH:MM:SS".
  • data_pool: data pool the subvolume belongs to.
  • path: absolute path of a subvolume.
  • type: subvolume type indicating whether it’s clone or subvolume.
  • pool_namespace: RADOS namespace of the subvolume.
  • features: features supported by the subvolume, such as , "snapshot-clone", "snapshot-autoprotect", or "snapshot-retention".
  • state: current state of the subvolume, such as, "complete" or "snapshot-retained"

5.2.6. Creating snapshot of a file system subvolume

This section shows how to create snapshots of Ceph File System (CephFS) subvolume.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • A CephFS subvolume.
  • In addition to read (r) and write (w) capabilities, clients also require s flag on a directory path within the file system.

Procedure

  1. Verify that the s flag is set on the directory:

    Syntax

    ceph auth get CLIENT_NAME

    Example

    client.0
        key: AQAz7EVWygILFRAAdIcuJ12opU/JKyfFmxhuaw==
        caps: [mds] allow rw, allow rws path=/bar 1
        caps: [mon] allow r
        caps: [osd] allow rw tag cephfs data=cephfs_a 2

    1 2
    In the example, client.0 can create or delete snapshots in the bar directory of file system cephfs_a.
  2. Create a snapshot of the Ceph File System subvolume:

    Syntax

    ceph fs subvolume snapshot create VOLUME_NAME _SUBVOLUME_NAME _SNAP_NAME [--group_name GROUP_NAME]

    Example

    [root@mon ~]# ceph fs subvolume snapshot create cephfs sub0 snap0 --group_name subgroup0

5.2.7. Cloning subvolumes from snapshots

Subvolumes can be created by cloning subvolume snapshots. It is an asynchronous operation involving copying data from a snapshot to a subvolume.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • To create or delete snapshots, in addition to read and write capability, clients require s flag on a directory path within the filesystem.

    Syntax

    CLIENT_NAME
        key: AQAz7EVWygILFRAAdIcuJ12opU/JKyfFmxhuaw==
        caps: [mds] allow rw, allow rws path=DIRECTORY_PATH
        caps: [mon] allow r
        caps: [osd] allow rw tag cephfs data=DIRECTORY_NAME

    In the following example, client.0 can create or delete snapshots in the bar directory of filesystem cephfs_a.

    Example

    client.0
        key: AQAz7EVWygILFRAAdIcuJ12opU/JKyfFmxhuaw==
        caps: [mds] allow rw, allow rws path=/bar
        caps: [mon] allow r
        caps: [osd] allow rw tag cephfs data=cephfs_a

Procedure

  1. Create a Ceph File System (CephFS) volume:

    Syntax

    ceph fs volume create VOLUME_NAME

    Example

    [root@mon ~]# ceph fs volume create cephfs

    This creates the CephFS file system, its data and metadata pools.

  2. Create a subvolume group. By default, the subvolume group is created with an octal file mode '755', and data pool layout of its parent directory.

    Syntax

    ceph fs subvolumegroup create VOLUME_NAME GROUP_NAME [--pool_layout DATA_POOL_NAME --uid UID --gid GID --mode OCTAL_MODE]

    Example

    [root@mon ~]# ceph fs subvolumegroup create cephfs subgroup0

  3. Create a subvolume. By default, a subvolume is created within the default subvolume group, and with an octal file mode ‘755’, uid of its subvolume group, gid of its subvolume group, data pool layout of its parent directory and no size limit.

    Syntax

    ceph fs subvolume create VOLUME_NAME SUBVOLUME_NAME [--size SIZE_IN_BYTES --group_name SUBVOLUME_GROUP_NAME --pool_layout DATA_POOL_NAME --uid _UID --gid GID --mode OCTAL_MODE]

    Example

    [root@mon ~]# ceph fs subvolume create cephfs sub0 --group_name subgroup0

  4. Create a snapshot of a subvolume:

    Syntax

    ceph fs subvolume snapshot create VOLUME_NAME _SUBVOLUME_NAME SNAP_NAME [--group_name SUBVOLUME_GROUP_NAME]

    Example

    [root@mon ~]# ceph fs subvolume snapshot create cephfs sub0 snap0  --group_name subgroup0

  5. Initiate a clone operation:

    Note

    By default, cloned subvolumes are created in the default group.

    1. If the source subvolume and the target clone are in the default group, run the following command:

      Syntax

      ceph fs subvolume snapshot clone VOLUME_NAME SUBVOLUME_NAME SNAP_NAME TARGET_SUBVOLUME_NAME

      Example

      [root@mon ~]# ceph fs subvolume snapshot clone cephfs sub0 snap0 clone0

    2. If the source subvolume is in the non-default group, then specify the source subvolume group in the following command:

      Syntax

      ceph fs subvolume snapshot clone VOLUME_NAME SUBVOLUME_NAME SNAP_NAME TARGET_SUBVOLUME_NAME --group_name SUBVOLUME_GROUP_NAME

      Example

      [root@mon ~]# ceph fs subvolume snapshot clone cephfs sub0 snap0 clone0 --group_name subgroup0

    3. If the target clone is to a non-default group, then specify the target group in the following command:

      Syntax

      ceph fs subvolume snapshot clone VOLUME_NAME SUBVOLUME_NAME SNAP_NAME TARGET_SUBVOLUME_NAME --target_group_name _SUBVOLUME_GROUP_NAME

      Example

      [root@mon ~]# ceph fs subvolume snapshot clone cephfs sub0 snap0 clone0 --target_group_name subgroup1

  6. Check the status of the clone operation:

    Syntax

    ceph fs clone status VOLUME_NAME CLONE_NAME [--group_name TARGET_GROUP_NAME]

    Example

    [root@mon ~]# ceph fs clone status cephfs clone0 --group_name subgroup1
    
    {
      "status": {
        "state": "complete"
      }
    }

Additional Resources

5.2.8. Listing snapshots of a file system subvolume

This section provides the step to list the snapshots of a Ceph File system (CephFS) subvolume.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • A CephFS subvolume.
  • Snapshots of the subvolume.

Procedure

  1. List the snapshots of a CephFS subvolume:

    Syntax

    ceph fs subvolume snapshot ls VOLUME_NAME SUBVOLUME_NAME [--group_name SUBVOLUME_GROUP_NAME]

    Example

    [root@mon ~]# ceph fs subvolume snapshot ls cephfs sub0 --group_name subgroup0

5.2.9. Fetching metadata of the snapshots of a file system subvolume

This section provides the step to fetch the metadata of the snapshots of a Ceph File system (CephFS) subvolume.

Prerequisites

  • A working Red Hat Ceph Storage cluster with CephFS deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • A CephFS subvolume.
  • Snapshots of the subvolume.

Procedure

  1. Fetch the metadata of the snapshots of a CephFS subvolume:

    Syntax

    ceph fs subvolume snapshot info VOLUME_NAME SUBVOLUME_NAME SNAP_NAME [--group_name SUBVOLUME_GROUP_NAME]

    Example

    [root@mon ~]# ceph fs subvolume snapshot info cephfs sub0 snap0 --group_name subgroup0

    Example output

    {
        "created_at": "2021-09-08 06:18:47.330682",
        "data_pool": "cephfs_data",
        "has_pending_clones": "no",
        "size": 0
    }

The output format is json and contains the following fields:

  • created_at: time of creation of snapshot in the format "YYYY-MM-DD HH:MM:SS:ffffff".
  • data_pool: data pool the snapshot belongs to.
  • has_pending_clones: "yes" if snapshot clone is in progress otherwise "no".
  • size: snapshot size in bytes.

5.2.10. Removing a file system subvolume

This section describes the step to remove the Ceph File system (CephFS) subvolume.

Note

The ceph fs subvolume rm command removes the subvolume and its contents in two steps. First, it moves the subvolume to a trash folder, and then asynchronously purges its contents.

A subvolume can be removed retaining existing snapshots of the subvolume using the --retain-snapshots option. If snapshots are retained, the subvolume is considered empty for all operations not involving the retained snapshots. Retained snapshots can be used as a clone source to recreate the subvolume, or cloned to a newer subvolume.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • A CephFS subvolume.

Procedure

  1. Remove a CephFS subvolume:

    Syntax

    ceph fs subvolume rm VOLUME_NAME SUBVOLUME_NAME [--group_name SUBVOLUME_GROUP_NAME] [--force] [--retain-snapshots]

    Example

    [root@mon ~]# ceph fs subvolume rm cephfs sub0 --group_name subgroup0 --retain snapshots

  2. To recreate a subvolume from a retained snapshot:

    Syntax

    ceph fs subvolume snapshot clone VOLUME_NAME DELETED_SUBVOLUME RETAINED_SNAPSHOT NEW_SUBVOLUME --group_name SUBVOLUME_GROUP_NAME --target_group_name SUBVOLUME_TARGET_GROUP_NAME

    *NEW_SUBVOLUME - can either be the same subvolume which was deleted earlier or clone it to a new subvolume.

    Example

    ceph fs subvolume snapshot clone cephfs sub0 snap0 sub1 --group_name subgroup0 --target_group_name subgroup0

5.2.11. Removing snapshot of a file system subvolume

This section provides the step to remove snapshots of a Ceph File system (CephFS) subvolume group.

Note

Using the --force flag allows the command to succeed that would otherwise fail if the snapshot did not exist.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • A Ceph File System volume.
  • A snapshot of the subvolume group.

Procedure

  1. Remove the snapshot of the CephFS subvolume:

    Syntax

    ceph fs subvolume snapshot rm VOLUME_NAME SUBVOLUME_NAME _SNAP_NAME [--group_name GROUP_NAME --force]

    Example

    [root@mon ~]# ceph fs subvolume snapshot rm cephfs sub0 snap0 --group_name subgroup0 --force

5.3. Ceph File System subvolume groups

As a storage administrator, you can create, list, fetch absolute path, and remove Ceph File System (CephFS) subvolume groups. Additionally, you can also create, list and remove snapshots of these subvolume groups. CephFS subvolume groups are abstractions at a directory level which effects policies, for example, file layouts, across a set of subvolumes.

This section describes how to:

5.3.1. Creating a file system subvolume group

This section describes how to create Ceph File system (CephFS) subvolume group.

Note

When creating a subvolume group you can specify its data pool layout, uid, gid, and file mode in octal numerals. By default, the subvolume group is created with an octal file mode ‘755’, uid ‘0’, gid ‘0’ and data pool layout of its parent directory.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.

Procedure

  1. Create a CephFS subvolume group:

    Syntax

    ceph fs subvolumegroup create VOLUME_NAME GROUP_NAME [--pool_layout DATA_POOL_NAME --uid UID --gid GID --mode OCTAL_MODE]

    Example

    [root@mon ~]# ceph fs subvolumegroup create cephfs subgroup0

    The command succeeds even if the subvolume group already exists.

5.3.2. Listing file system subvolume groups

This section describes the step to list the Ceph File system (CephFS) subvolume groups.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • A CephFS subvolume group.

Procedure

  1. List the CephFS subvolume groups:

    Syntax

    ceph fs subvolumegroup ls VOLUME_NAME

    Example

    [root@mon ~]# ceph fs subvolumegroup ls cephfs

5.3.3. Fetching absolute path of a file system subvolume group

This section shows how to fetch the absolute path of a Ceph File system (CephFS) subvolume group.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • A CephFS subvolume group.

Procedure

  1. Fetch the absolute path of the CephFS subvolume group:

    Syntax

    ceph fs subvolumegroup getpath VOLUME_NAME GROUP_NAME

    Example

    [root@mon ~]# ceph fs subvolumegroup getpath cephfs subgroup0

5.3.4. Creating snapshot of a file system subvolume group

This section shows how to create snapshots of Ceph File system (CephFS) subvolume group.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • CephFS subvolume group.
  • In addition to read (r) and write (w) capabilities, clients also require s flag on a directory path within the file system.

Procedure

  1. Verify that the s flag is set on the directory:

    Syntax

    ceph auth get CLIENT_NAME

    Example

    client.0
        key: AQAz7EVWygILFRAAdIcuJ12opU/JKyfFmxhuaw==
        caps: [mds] allow rw, allow rws path=/bar 1
        caps: [mon] allow r
        caps: [osd] allow rw tag cephfs data=cephfs_a 2

    1 2
    In the example, client.0 can create or delete snapshots in the bar directory of file system cephfs_a.
  2. Create a snapshot of the CephFS subvolume group:

    Syntax

    ceph fs subvolumegroup snapshot create VOLUME_NAME _GROUP_NAME SNAP_NAME

    Example

    [root@mon ~]# ceph fs subvolumegroup snapshot create cephfs subgroup0 snap0

    The command implicitly snapshots all the subvolumes under the subvolume group.

5.3.5. Listing snapshots of a file system subvolume group

This section provides the steps to list the snapshots of a Ceph File system (CephFS) subvolume group.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • A CephFS subvolume group.
  • Snapshots of the subvolume group.

Procedure

  1. List the snapshots of a CephFS subvolume group:

    Syntax

    ceph fs subvolumegroup snapshot ls VOLUME_NAME GROUP_NAME

    Example

    [root@mon ~]# ceph fs subvolumegroup snapshot ls cephfs subgroup0

5.3.6. Removing snapshot of a file system subvolume group

This section provides the step to remove snapshots of a Ceph File system (CephFS) subvolume group.

Note

Using the --force flag allows the command to succeed that would otherwise fail if the snapshot did not exist.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • A Ceph File System volume.
  • A snapshot of the subvolume group.

Procedure

  1. Remove the snapshot of the CephFS subvolume group:

    Syntax

    ceph fs subvolumegroup snapshot rm VOLUME_NAME GROUP_NAME SNAP_NAME [--force]

    Example

    [root@mon ~]# ceph fs subvolumegroup snapshot rm cephfs subgroup0 snap0 --force

5.3.7. Removing a file system subvolume group

This section shows how to remove the Ceph File system (CephFS) subvolume group.

Note

The removal of a subvolume group fails if it is not empty or non-existent. The --force flag allows the non-existent subvolume group to be removed.

Prerequisites

  • A working Red Hat Ceph Storage cluster with Ceph File System deployed.
  • At least read access on the Ceph Monitor.
  • Read and write capability on the Ceph Manager nodes.
  • A CephFS subvolume group.

Procedure

  1. Remove the CephFS subvolume group:

    Syntax

    ceph fs subvolumegroup rm VOLUME_NAME GROUP_NAME [--force]

    Example

    [root@mon ~]# ceph fs subvolumegroup rm cephfs subgroup0 --force

5.4. Additional Resources

Appendix A. Health messages for the Ceph File System

Cluster health checks

The Ceph Monitor daemons generate health messages in response to certain states of the Metadata Server (MDS). Below is the list of the health messages and their explanation:

mds rank(s) <ranks> have failed
One or more MDS ranks are not currently assigned to any MDS daemon. The storage cluster will not recover until a suitable replacement daemon starts.
mds rank(s) <ranks> are damaged
One or more MDS ranks has encountered severe damage to its stored metadata, and cannot start again until the metadata is repaired.
mds cluster is degraded
One or more MDS ranks are not currently up and running, clients might pause metadata I/O until this situation is resolved. This includes ranks being failed or damaged, and includes ranks which are running on an MDS but are not in the active state yet — for example, ranks in the replay state.
mds <names> are laggy
The MDS daemons are supposed to send beacon messages to the monitor in an interval specified by the mds_beacon_interval option, the default is 4 seconds. If an MDS daemon fails to send a message within the time specified by the mds_beacon_grace option, the default is 15 seconds. The Ceph Monitor marks the MDS daemon as laggy and automatically replaces it with a standby daemon if any is available.

Daemon-reported health checks

The MDS daemons can identify a variety of unwanted conditions, and return them in the output of the ceph status command. These conditions have human readable messages, and also have a unique code starting MDS_HEALTH, which appears in JSON output. Below is the list of the daemon messages, their codes, and explanation.

"Behind on trimming…​"

Code: MDS_HEALTH_TRIM

CephFS maintains a metadata journal that is divided into log segments. The length of journal (in number of segments) is controlled by the mds_log_max_segments setting. When the number of segments exceeds that setting, the MDS starts writing back metadata so that it can remove (trim) the oldest segments. If this process is too slow, or a software bug is preventing trimming, then this health message appears. The threshold for this message to appear is for the number of segments to be double mds_log_max_segments.

"Client <name> failing to respond to capability release"

Code: MDS_HEALTH_CLIENT_LATE_RELEASE, MDS_HEALTH_CLIENT_LATE_RELEASE_MANY

CephFS clients are issued capabilities by the MDS. The capabilities work like locks. Sometimes, for example when another client needs access, the MDS requests clients to release their capabilities. If the client is unresponsive, it might fail to do so promptly, or fail to do so at all. This message appears if a client has taken a longer time to comply than the time specified by the mds_revoke_cap_timeout option (default is 60 seconds).

"Client <name> failing to respond to cache pressure"

Code: MDS_HEALTH_CLIENT_RECALL, MDS_HEALTH_CLIENT_RECALL_MANY

Clients maintain a metadata cache. Items, such as inodes, in the client cache are also pinned in the MDS cache. When the MDS needs to shrink its cache to stay within its own cache size limits, the MDS sends messages to clients to shrink their caches too. If a client is unresponsive, it can prevent the MDS from properly staying within its cache size, and the MDS might eventually run out of memory and terminate unexpectedly. This message appears if a client has taken more time to comply than the time specified by the mds_recall_state_timeout option (default is 60 seconds). See Understanding MDS Cache Size Limits for details.

"Client name failing to advance its oldest client/flush tid"

Code: MDS_HEALTH_CLIENT_OLDEST_TID, MDS_HEALTH_CLIENT_OLDEST_TID_MANY

The CephFS protocol for communicating between clients and MDS servers uses a field called oldest tid to inform the MDS of which client requests are fully complete so that the MDS can forget about them. If an unresponsive client is failing to advance this field, the MDS might be prevented from properly cleaning up resources used by client requests. This message appears if a client has more requests than the number specified by the max_completed_requests option (default is 100000) that are complete on the MDS side but have not yet been accounted for in the client’s oldest tid value.

"Metadata damage detected"

Code: MDS_HEALTH_DAMAGE

Corrupt or missing metadata was encountered when reading from the metadata pool. This message indicates that the damage was sufficiently isolated for the MDS to continue operating, although client accesses to the damaged subtree return I/O errors. Use the damage ls administration socket command to view details on the damage. This message appears as soon as any damage is encountered.

"MDS in read-only mode"

Code: MDS_HEALTH_READ_ONLY

The MDS has entered into read-only mode and will return the EROFS error codes to client operations that attempt to modify any metadata. The MDS enters into read-only mode:

  • If it encounters a write error while writing to the metadata pool.
  • If the administrator forces the MDS to enter into read-only mode by using the force_readonly administration socket command.
"<N> slow requests are blocked"

Code: MDS_HEALTH_SLOW_REQUEST

One or more client requests have not been completed promptly, indicating that the MDS is either running very slowly, or encountering a bug. Use the ops administration socket command to list outstanding metadata operations. This message appears if any client requests have taken more time than the value specified by the mds_op_complaint_time option (default is 30 seconds).

"Too many inodes in cache"
Code: MDS_HEALTH_CACHE_OVERSIZED

The MDS has failed to trim its cache to comply with the limit set by the administrator. If the MDS cache becomes too large, the daemon might exhaust available memory and terminate unexpectedly. By default, this message appears if the MDS cache size is 50% greater than its limit.

Additional Resources

Appendix B. Metadata Server daemon configuration Reference

Refer the list commands that can be used for Metadata Server (MDS) daemon configuration.

mon_force_standby_active
Description
If set to true, monitors force MDS in standby replay mode to be active. Set under the [mon] or [global] section in the Ceph configuration file.
Type
Boolean
Default
true
max_mds
Description
The number of active MDS daemons during cluster creation. Set under the [mon] or [global] section in the Ceph configuration file.
Type
32-bit Integer
Default
1
mds_cache_memory_limit
Description
The memory limit the MDS enforces for its cache. Red Hat recommends to use this parameter instead of the mds cache size parameter.
Type
64-bit Integer Unsigned
Default
1073741824
mds_cache_reservation
Description
The cache reservation, memory or inodes, for the MDS cache to maintain. The value is a percentage of the maximum cache configured. Once the MDS begins dipping into its reservation, it recalls client state until its cache size shrinks to restore the reservation.
Type
Float
Default
0.05
mds_cache_size
Description
The number of inodes to cache. A value of 0 indicates an unlimited number. Red Hat recommends to use the mds_cache_memory_limit to limit the amount of memory the MDS cache uses.
Type
32-bit Integer
Default
0
mds_cache_mid
Description
The insertion point for new items in the cache LRU, from the top.
Type
Float
Default
0.7
mds_dir_commit_ratio
Description
The fraction of directory contains erroneous information before Ceph commits using a full update, instead of partial update.
Type
Float
Default
0.5
mds_dir_max_commit_size
Description
The maximum size of a directory update before Ceph breaks the directory into smaller transactions, in MB.
Type
32-bit Integer
Default
90
mds_decay_halflife
Description
The half-life of MDS cache temperature.
Type
Float
Default
5
mds_beacon_interval
Description
The frequency, in seconds, of beacon messages sent to the monitor.
Type
Float
Default
4
mds_beacon_grace
Description
The interval without beacons before Ceph declares an MDS laggy, and possibly replace it.
Type
Float
Default
15
mds_blacklist_interval
Description
The blacklist duration for failed MDS daemons in the OSD map.
Type
Float
Default
24.0*60.0
mds_session_timeout
Description
The interval, in seconds, of client inactivity before Ceph times out capabilities and leases.
Type
Float
Default
60
mds_session_autoclose
Description
The interval, in seconds, before Ceph closes a laggy client’s session.
Type
Float
Default
300
mds_reconnect_timeout
Description
The interval, in seconds, to wait for clients to reconnect during MDS restart.
Type
Float
Default
45
mds_tick_interval
Description
How frequently the MDS performs internal periodic tasks.
Type
Float
Default
5
mds_dirstat_min_interval
Description
The minimum interval, in seconds, to try to avoid propagating recursive statistics up the tree.
Type
Float
Default
1
mds_scatter_nudge_interval
Description
How quickly changes in directory statistics propagate up.
Type
Float
Default
5
mds_client_prealloc_inos
Description
The number of inode numbers to preallocate per client session.
Type
32-bit Integer
Default
1000
mds_early_reply
Description
Determines whether the MDS allows clients to see request results before they commit to the journal.
Type
Boolean
Default
true
mds_use_tmap
Description
Use trivialmap for directory updates.
Type
Boolean
Default
true
mds_default_dir_hash
Description
The function to use for hashing files across directory fragments.
Type
32-bit Integer
Default
2,that is, rjenkins
mds_log
Description
Set to true if the MDS should journal metadata updates. Disable for benchmarking only.
Type
Boolean
Default
true
mds_log_skip_corrupt_events
Description
Determines whether the MDS tries to skip corrupt journal events during journal replay.
Type
Boolean
Default
false
mds_log_max_events
Description
The maximum events in the journal before Ceph initiates trimming. Set to -1 to disable limits.
Type
32-bit Integer
Default
-1
mds_log_max_segments
Description
The maximum number of segments or objects, in the journal before Ceph initiates trimming. Set to -1 to disable limits.
Type
32-bit Integer
Default
30
mds_log_max_expiring
Description
The maximum number of segments to expire in parallels.
Type
32-bit Integer
Default
20
mds_log_eopen_size
Description
The maximum number of inodes in an EOpen event.
Type
32-bit Integer
Default
100
mds_bal_sample_interval
Description
Determines how frequently to sample directory temperature, when making fragmentation decisions.
Type
Float
Default
3
mds_bal_replicate_threshold
Description
The maximum temperature before Ceph attempts to replicate metadata to other nodes.
Type
Float
Default
8000
mds_bal_unreplicate_threshold
Description
The minimum temperature before Ceph stops replicating metadata to other nodes.
Type
Float
Default
0
mds_bal_frag
Description
Determines whether the MDS fragments directories.
Type
Boolean
Default
false
mds_bal_split_size
Description
The maximum directory size before the MDS splits a directory fragment into smaller bits. The root directory has a default fragment size limit of 10000.
Type
32-bit Integer
Default
10000
mds_bal_split_rd
Description
The maximum directory read temperature before Ceph splits a directory fragment.
Type
Float
Default
25000
mds_bal_split_wr
Description
The maximum directory write temperature before Ceph splits a directory fragment.
Type
Float
Default
10000
mds_bal_split_bits
Description
The number of bits by which to split a directory fragment.
Type
32-bit Integer
Default
3
mds_bal_merge_size
Description
The minimum directory size before Ceph tries to merge adjacent directory fragments.
Type
32-bit Integer
Default
50
mds_bal_merge_rd
Description
The minimum read temperature before Ceph merges adjacent directory fragments.
Type
Float
Default
1000
mds_bal_merge_wr
Description
The minimum write temperature before Ceph merges adjacent directory fragments.
Type
Float
Default
1000
mds_bal_interval
Description
The frequency, in seconds, of workload exchanges between MDS nodes.
Type
32-bit Integer
Default
10
mds_bal_fragment_interval
Description
The frequency, in seconds, of adjusting directory fragmentation.
Type
32-bit Integer
Default
5
mds_bal_idle_threshold
Description
The minimum temperature before Ceph migrates a subtree back to its parent.
Type
Float
Default
0
mds_bal_max
Description
The number of iterations to run balancer before Ceph stops. For testing purposes only.
Type
32-bit Integer
Default
-1
mds_bal_max_until
Description
The number of seconds to run balancer before Ceph stops. For testing purposes only.
Type
32-bit Integer
Default
-1
mds_bal_mode
Description

The method for calculating MDS load:

  • 1 = Hybrid.
  • 2 = Request rate and latency.
  • 3 = CPU load.
Type
32-bit Integer
Default
0
mds_bal_min_rebalance
Description
The minimum subtree temperature before Ceph migrates.
Type
Float
Default
0.1
mds_bal_min_start
Description
The minimum subtree temperature before Ceph searches a subtree.
Type
Float
Default
0.2
mds_bal_need_min
Description
The minimum fraction of target subtree size to accept.
Type
Float
Default
0.8
mds_bal_need_max
Description
The maximum fraction of target subtree size to accept.
Type
Float
Default
1.2
mds_bal_midchunk
Description
Ceph migrates any subtree that is larger than this fraction of the target subtree size.
Type
Float
Default
0.3
mds_bal_minchunk
Description
Ceph ignores any subtree that is smaller than this fraction of the target subtree size.
Type
Float
Default
0.001
mds_bal_target_removal_min
Description
The minimum number of balancer iterations before Ceph removes an old MDS target from the MDS map.
Type
32-bit Integer
Default
5
mds_bal_target_removal_max
Description
The maximum number of balancer iterations before Ceph removes an old MDS target from the MDS map.
Type
32-bit Integer
Default
10
mds_replay_interval
Description
The journal poll interval when in standby-replay mode for a hot standby.
Type
Float
Default
1
mds_shutdown_check
Description
The interval for polling the cache during MDS shutdown.
Type
32-bit Integer
Default
0
mds_thrash_exports
Description
Ceph randomly exports subtrees between nodes. For testing purposes only.
Type
32-bit Integer
Default
0
mds_thrash_fragments
Description
Ceph randomly fragments or merges directories.
Type
32-bit Integer
Default
0
mds_dump_cache_on_map
Description
Ceph dumps the MDS cache contents to a file on each MDS map.
Type
Boolean
Default
false
mds_dump_cache_after_rejoin
Description
Ceph dumps MDS cache contents to a file after rejoining the cache during recovery.
Type
Boolean
Default
false
mds_verify_scatter
Description
Ceph asserts that various scatter/gather invariants are true. For developer use only.
Type
Boolean
Default
false
mds_debug_scatterstat
Description
Ceph asserts that various recursive statistics invariants are true. For developer use only.
Type
Boolean
Default
false
mds_debug_frag
Description
Ceph verifies directory fragmentation invariants when convenient. For developer use only.
Type
Boolean
Default
false
mds_debug_auth_pins
Description
The debug authentication pin invariants. For developer use only.
Type
Boolean
Default
false
mds_debug_subtrees
Description
Debugging subtree invariants. For developer use only.
Type
Boolean
Default
false
mds_kill_mdstable_at
Description
Ceph injects MDS failure in MDS Table code. For developer use only.
Type
32-bit Integer
Default
0
mds_kill_export_at
Description
Ceph injects MDS failure in the subtree export code. For developer use only.
Type
32-bit Integer
Default
0
mds_kill_import_at
Description
Ceph injects MDS failure in the subtree import code. For developer use only.
Type
32-bit Integer
Default
0
mds_kill_link_at
Description
Ceph injects MDS failure in hard link code. For developer use only.
Type
32-bit Integer
Default
0
mds_kill_rename_at
Description
Ceph injects MDS failure in the rename code. For developer use only.
Type
32-bit Integer
Default
0
mds_wipe_sessions
Description
Ceph deletes all client sessions on startup. For testing purposes only.
Type
Boolean
Default
0
mds_wipe_ino_prealloc
Description
Ceph deletea inode preallocation metadata on startup. For testing purposes only.
Type
Boolean
Default
0
mds_skip_ino
Description
The number of inode numbers to skip on startup. For testing purposes only.
Type
32-bit Integer
Default
0
mds_standby_for_name
Description
The MDS daemon is a standby for another MDS daemon of the name specified in this setting.
Type
String
Default
N/A
mds_standby_for_rank
Description
An instance of the MDS daemon is a standby for another MDS daemon instance of this rank.
Type
32-bit Integer
Default
-1
mds_standby_replay
Description
Determines whether the MDS daemon polls and replays the log of an active MDS when used as a hot standby.
Type
Boolean
Default
false

Appendix C. Journaler configuration reference

Reference of the list commands that can be used for journaler configuration.

journaler_write_head_interval
Description
How frequently to update the journal head object.
Type
Integer
Required
No
Default
15
journaler_prefetch_periods
Description
How many stripe periods to read ahead on journal replay.
Type
Integer
Required
No
Default
10
journal_prezero_periods
Description
How many stripe periods to zero ahead of write position.
Type
Integer
Required
No
Default
10
journaler_batch_interval
Description
Maximum additional latency in seconds to incur artificially.
Type
Double
Required
No
Default
.001
journaler_batch_max
Description
Maximum bytes that will be delayed flushing.
Type
64-bit Unsigned Integer
Required
No
Default
0

Appendix D. Ceph File System client configuration reference

This section lists configuration options for Ceph File System (CephFS) FUSE clients. Set them in the Ceph configuration file under the [client] section.

client_acl_type
Description
Set the ACL type. Currently, only possible value is posix_acl to enable POSIX ACL, or an empty string. This option only takes effect when the fuse_default_permissions is set to false.
Type
String
Default
"" (no ACL enforcement)
client_cache_mid
Description
Set the client cache midpoint. The midpoint splits the least recently used lists into a hot and warm list.
Type
Float
Default
0.75
client_cache size
Description
Set the number of inodes that the client keeps in the metadata cache.
Type
Integer
Default
16384 (16 MB)
client_caps_release_delay
Description
Set the delay between capability releases in seconds. The delay sets how many seconds a client waits to release capabilities that it no longer needs in case the capabilities are needed for another user space operation.
Type
Integer
Default
5 (seconds)
client_debug_force_sync_read
Description
If set to true, clients read data directly from OSDs instead of using a local page cache.
Type
Boolean
Default
false
client_dirsize_rbytes
Description
If set to true, use the recursive size of a directory (that is, total of all descendants).
Type
Boolean
Default
true
client_max_inline_size
Description
Set the maximum size of inlined data stored in a file inode rather than in a separate data object in RADOS. This setting only applies if the inline_data flag is set on the MDS map.
Type
Integer
Default
4096
client_metadata
Description
Comma-delimited strings for client metadata sent to each MDS, in addition to the automatically generated version, host name, and other metadata.
Type
String
Default
"" (no additional metadata)
client_mount_gid
Description
Set the group ID of CephFS mount.
Type
Integer
Default
-1
client_mount_timeout
Description
Set the timeout for CephFS mount in seconds.
Type
Float
Default
300.0
client_mount_uid
Description
Set the user ID of CephFS mount.
Type
Integer
Default
-1
client_mountpoint
Description
An alternative to the -r option of the ceph-fuse command.
Type
String
Default
/
client_oc
Description
Enable object caching.
Type
Boolean
Default
true
client_oc_max_dirty
Description
Set the maximum number of dirty bytes in the object cache.
Type
Integer
Default
104857600 (100MB)
client_oc_max_dirty_age
Description
Set the maximum age in seconds of dirty data in the object cache before writeback.
Type
Float
Default
5.0 (seconds)
client_oc_max_objects
Description
Set the maximum number of objects in the object cache.
Type
Integer
Default
1000
client_oc_size
Description
Set how many bytes of data will the client cache.
Type
Integer
Default
209715200 (200 MB)
client_oc_target_dirty
Description
Set the target size of dirty data. Red Hat recommends to keep this number low.
Type
Integer
Default
8388608 (8MB)
client_permissions
Description
Check client permissions on all I/O operations.
Type
Boolean
Default
true
client_quota_df
Description
Report root directory quota for the statfs operation.
Type
Boolean
Default
true
client_readahead_max_bytes
Description
Set the maximum number of bytes that the kernel reads ahead for future read operations. Overridden by the client_readahead_max_periods setting.
Type
Integer
Default
0 (unlimited)
client_readahead_max_periods
Description
Set the number of file layout periods (object size * number of stripes) that the kernel reads ahead. Overrides the client_readahead_max_bytes setting.
Type
Integer
Default
4
client_readahead_min
Description
Set the minimum number bytes that the kernel reads ahead.
Type
Integer
Default
131072 (128KB)
client_snapdir
Description
Set the snapshot directory name.
Type
String
Default
".snap"
client_tick_interval
Description
Set the interval in seconds between capability renewal and other upkeep.
Type
Float
Default
1.0
client_use_random_mds
Description
Choose random MDS for each request.
Type
Boolean
Default
false
fuse_default_permissions
Description
When set to false, the ceph-fuse utility checks does its own permissions checking, instead of relying on the permissions enforcement in FUSE. Set to false together with the client acl type=posix_acl option to enable POSIX ACL.
Type
Boolean
Default
true
Developer Options

These options are internal. They are listed here only to complete the list of options.

client_debug_getattr_caps
Description
Check if the reply from the MDS contains required capabilities.
Type
Boolean
Default
false
client_debug_inject_tick_delay
Description
Add artificial delay between client ticks.
Type
Integer
Default
0
client_inject_fixed_oldest_tid
Description, Type
Boolean
Default
false
client_inject_release_failure
Description, Type
Boolean
Default
false
client_trace
Description
The path to the trace file for all file operations. The output is designed to be used by the Ceph synthetic client. See the ceph-syn(8) manual page for details.
Type
String
Default
"" (disabled)

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