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Chapter 5. Mirroring Ceph block devices

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

5.1. Prerequisites

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

5.2. Ceph block device mirroring

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

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

Important

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

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

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

A pool with the same name exists on both storage clusters.

A pool contains journal-enabled images you want to mirror.

Important

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

One-way Replication

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

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

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

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

Two-way Replication

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

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

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

Note

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

Mirroring Modes

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

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

Image States

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

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

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

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

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

Additional Resources

See the Image promotion and demotion section of the Red Hat Ceph Storage Block Device Guide for more details.

5.3. Configuring one-way mirroring using Ansible

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

Prerequisites

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

Note

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

Procedure

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

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

Syntax

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

Example

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

For existing images, use the rbd feature enable command:

Syntax

rbd feature enable POOL_NAME/IMAGE_NAME FEATURE_NAME

Example

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

To enable exclusive-lock and journaling on all new images by default, add the following setting to the Ceph configuration file:
```
rbd_default_features = 125
```

In the site-a cluster, complete the following steps:
1. On a monitor node, create the user that the rbd-mirror daemon will use to connect to the cluster. The example creates a site-a user and outputs the key to a file named site-a.client.site-a.keyring:
  Syntax
```
ceph auth get-or-create client.CLUSTER_NAME mon 'profile rbd' osd 'profile rbd pool=data' -o /etc/ceph/CLUSTER_NAME.client.USER_NAME.keyring
```
  Example
```
[root@mon ~]# ceph auth get-or-create client.site-a mon 'profile rbd' osd 'profile rbd pool=data' -o /etc/ceph/site-a.client.site-a.keyring
```
2. Copy the Ceph configuration file and the newly created key file from the monitor node to the site-b monitor and client nodes.
3. Rename the Ceph configuration file from ceph.conf to CLUSTER-NAME.conf. In these examples, the file is /etc/ceph/site-a.conf.
In the site-b cluster, complete the following steps:
1. On the Ansible administration node, add an [rbdmirrors] group in the Ansible inventory file. The usual inventory file is /etc/ansible/hosts.
2. Under the [rbdmirrors] group, add the name of the site-b client node on which the rbd-mirror daemon will run. The daemon will pull image changes from site-a to site-b.
```
[rbdmirrors]
ceph-client
```
3. Navigate to the /usr/share/ceph-ansible/ directory:
```
[root@admin ~]# cd /usr/share/ceph-ansible
```
4. Create a new rbdmirrors.yml file by copying group_vars/rbdmirrors.yml.sample to group_vars/rbdmirrors.yml:
```
[root@admin ceph-ansible]# cp group_vars/rbdmirrors.yml.sample group_vars/rbdmirrors.yml
```
5. Open the group_vars/rbdmirrors.yml file for editing.
6. Set ceph_rbd_mirror_configure to true. Set ceph_rbd_mirror_pool to the pool in which you want to mirror images. In these examples, data is the name of the pool.
```
ceph_rbd_mirror_configure: true
ceph_rbd_mirror_pool: "data"
```
7. By default, ceph-ansible configures mirroring using pool mode, which mirrors all images in a pool. Enable image mode where only images that have mirroring explicitly enabled are mirrored. To enable image mode, set ceph_rbd_mirror_mode to image:
```
ceph_rbd_mirror_mode: image
```
8. Set a name for the cluster that rbd-mirror will pull from. In these examples, the other cluster is site-a.
```
ceph_rbd_mirror_remote_cluster: "site-a"
```
9. On the Ansible administration node, set the user name of the key using ceph_rbd_mirror_remote_user. Use the same name you used when you created the key. In these examples the user is named client.site-a.
```
ceph_rbd_mirror_remote_user: "client.site-a"
```
10. As the ceph-ansible user, run the Ansible playbook:
  - Bare-metal deployments:
    [user@admin ceph-ansible]$ ansible-playbook site.yml --limit rbdmirrors -i hosts
  - Container deployments:
    [ansible@admin ceph-ansible]$ ansible-playbook site-container.yml --limit rbdmirrors -i hosts
Explicitly enable mirroring on the desired images in both site-a and site-b clusters:
Syntax
Journal-based mirroring:
```
rbd mirror image enable POOL/IMAGE
```
Snapshot-based mirroring:
```
rbd mirror image enable POOL/IMAGE snapshot
```
Example
```
[root@mon ~]# rbd mirror image enable data/image1
[root@mon ~]# rbd mirror image enable data/image1 snapshot
```
Note
Repeat this step whenever you want to mirror new image to peer cluster.

Verify the mirroring status. Run the following command from a Ceph Monitor node in the site-b cluster:

Example

Journal-based mirroring:

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

Snapshot-based mirroring:

[root@mon ~]# rbd mirror image status data/image1
image1:
  global_id:   06acc9e6-a63d-4aa1-bd0d-4f3a79b0ae33
  state:       up+replaying 1
  description: replaying, {"bytes_per_second":0.0,"bytes_per_snapshot":0.0,"local_snapshot_timestamp":1642689843,"remote_snapshot_timestamp":1642689843,"replay_state":"idle"}
  service:     admin on ceph-rbd2-vasi-43-5hwia4-node2
  last_update: 2022-01-20 12:41:57

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

Note

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

5.4. Configuring two-way mirroring using Ansible

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

Note

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

Prerequisites

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

Procedure

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

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

Syntax

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

Example

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

For existing images, use the rbd feature enable command:

Syntax

rbd feature enable POOL_NAME/IMAGE_NAME FEATURE_NAME

Example

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

To enable exclusive-lock and journaling on all new images by default, add the following setting to the Ceph configuration file:
```
rbd_default_features = 125
```

In the site-a cluster, complete the following steps:

On a monitor node, create the user the rbd-mirror daemon will use to connect to the cluster. The example creates a site-a user and outputs the key to a file named site-a.client.site-a.keyring, and the Ceph configuration file is /etc/ceph/site-a.conf.

Syntax

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

Example

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

Copy the keyring to the site-b cluster. Copy the file to the client node in the site-b cluster that the rbd-daemon will run on. Save the file to /etc/ceph/site-a.client.site-a.keyring:

Syntax

scp /etc/ceph/PRIMARY_CLUSTER_NAME.client.USER_NAME.keyring root@SECONDARY_CLIENT_NODE_NAME:/etc/ceph/PRIMARY_CLUSTER_NAME.client.USER_NAME.keyring

Example

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

Copy the Ceph configuration file from the monitor node to the site-b monitor node and client nodes. The Ceph configuration file in this example is /etc/ceph/site-a.conf.

Syntax

scp /etc/ceph/PRIMARY_CLUSTER_NAME.conf root@SECONDARY_MONITOR_NODE_NAME:/etc/ceph/PRIMARY_CLUSTER_NAME.conf
scp /etc/ceph/PRIMARY_CLUSTER_NAME.conf user@SECONDARY_CLIENT_NODE_NAME:/etc/ceph/PRIMARY_CLUSTER_NAME.conf

Example

[root@mon ~]# scp /etc/ceph/site-a.conf root@mon.site-b:/etc/ceph/site-a.conf
[root@mon ~]# scp /etc/ceph/site-a.conf user@client.site-b:/etc/ceph/site-a.conf

In the site-b cluster, complete the following steps:
1. Configure mirroring from site-a to site-b. On the Ansible administration node, add an [rbdmirrors] group in the Ansible inventory file, usually /usr/share/ceph-ansible/hosts.
2. Under the [rbdmirrors] group, add the name of a site-b client node that the rbd-mirror daemon will run on. This daemon pulls image changes from site-a to site-b.
  Example
```
[rbdmirrors]
client.site-b
```
3. Navigate to the /usr/share/ceph-ansible/ directory:
```
[root@admin ~]$ cd /usr/share/ceph-ansible
```
4. Create a new rbdmirrors.yml file by copying group_vars/rbdmirrors.yml.sample to group_vars/rbdmirrors.yml:
```
[root@admin ceph-ansible]# cp group_vars/rbdmirrors.yml.sample group_vars/rbdmirrors.yml
```
5. Open for editing the group_vars/rbdmirrors.yml file.
6. Set ceph_rbd_mirror_configure to true, and set ceph_rbd_mirror_pool to the pool you want to mirror images in. In these examples, data is the name of the pool.
```
ceph_rbd_mirror_configure: true
ceph_rbd_mirror_pool: "data"
```
7. By default, ceph-ansible configures mirroring using pool mode, which mirrors all images in a pool. Enable image mode where only images that have mirroring explicitly enabled are mirrored. To enable image mode, set ceph_rbd_mirror_mode to image:
```
ceph_rbd_mirror_mode: image
```
8. Set a name for the cluster that rbd-mirror in the group_vars/rbdmirrors.yml file. In these examples, the other cluster is site-a.
```
ceph_rbd_mirror_remote_cluster: "site-a"
```
9. On the Ansible administration node, set the user name of the key using ceph_rbd_mirror_remote_user in the group_vars/rbdmirrors.yml file. Use the same name you used when you created the key. In these examples the user is named client.site-a.
```
ceph_rbd_mirror_remote_user: "client.site-a"
```
10. As the ansible user, run the Ansible playbook:
  - Bare-metal deployments:
    [user@admin ceph-ansible]$ ansible-playbook site.yml --limit rbdmirrors -i hosts
  - Container deployments:
    [user@admin ceph-ansible]$ ansible-playbook site-container.yml --limit rbdmirrors -i hosts

Verify the mirroring status. Run the following command from a Ceph Monitor node on the site-b cluster:

Example

Journal-based mirroring:

[root@mon ~]# rbd mirror image status data/image1
image1:
  global_id:   7d486c3f-d5a1-4bee-ae53-6c4f1e0c8eac
  state:       up+replaying 1
  description: replaying, master_position=[object_number=3, tag_tid=1, entry_tid=3], mirror_position=[object_number=3, tag_tid=1, entry_tid=3], entries_behind_master=0
  last_update: 2021-04-22 13:19:27

Snapshot-based mirroring:

[root@mon ~]# rbd mirror image status data/image1
image1:
  global_id:   06acc9e6-a63d-4aa1-bd0d-4f3a79b0ae33
  state:       up+replaying 1
  description: replaying, {"bytes_per_second":0.0,"bytes_per_snapshot":0.0,"local_snapshot_timestamp":1642689843,"remote_snapshot_timestamp":1642689843,"replay_state":"idle"}
  service:     admin on ceph-rbd2-vasi-43-5hwia4-node2
  last_update: 2022-01-20 12:41:57

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

Note

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

In the site-b cluster, complete the following steps. The steps are largely the same as above:

On a monitor node, create the user the rbd-mirror daemon will use to connect to the cluster. The example creates a site-b user and outputs the key to a file named site-b.client.site-b.keyring, and the Ceph configuration file is /etc/ceph/site-b.conf.

Syntax

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

Example

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

Copy the keyring to the site-a cluster. Copy the file to the client node in the site-a cluster that the rbd-daemon will run on. Save the file to /etc/ceph/site-b.client.site-b.keyring:

Syntax

scp /etc/ceph/SECONDARY_CLUSTER_NAME.client.USER_NAME.keyring root@PRIMARY_CLIENT_NODE_NAME:/etc/ceph/SECONDARY_CLUSTER_NAME.client.USER_NAME.keyring

Example

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

Copy the Ceph configuration file from the monitor node to the site-a monitor node and client nodes. The Ceph configuration file in this example is /etc/ceph/site-b.conf.

Syntax

scp /etc/ceph/SECONDARY_CLUSTER_NAME.conf root@PRIMARY_MONITOR_NODE_NAME:/etc/ceph/SECONDARY_CLUSTER_NAME.conf
scp /etc/ceph/SECONDARY_CLUSTER_NAME.conf user@PRIMARY_CLIENT_NODE_NAME:/etc/ceph/SECONDARY_CLUSTER_NAME.conf

Example

[root@mon ~]# scp /etc/ceph/site-b.conf root@mon.site-a:/etc/ceph/site-b.conf
[root@mon ~]# scp /etc/ceph/site-b.conf user@client.site-a:/etc/ceph/site-b.conf

In the site-a cluster, complete the following steps:
1. Configure mirroring from site-b to site-a. On the Ansible administration node, add an [rbdmirrors] group in the Ansible inventory file, usually /usr/share/ceph-ansible/hosts.
2. Under the [rbdmirrors] group, add the name of a site-a client node that the rbd-mirror daemon will run on. This daemon pulls image changes from site-b to site-a.
  Example
```
[rbdmirrors]
client.site-a
```
3. Navigate to the /usr/share/ceph-ansible/ directory:
```
[root@admin ~]# cd /usr/share/ceph-ansible
```
4. Create a new rbdmirrors.yml file by copying group_vars/rbdmirrors.yml.sample to group_vars/rbdmirrors.yml:
```
[root@admin ceph-ansible]# cp group_vars/rbdmirrors.yml.sample group_vars/rbdmirrors.yml
```
5. Open for editing the group_vars/rbdmirrors.yml file.
6. Set ceph_rbd_mirror_configure to true, and set ceph_rbd_mirror_pool to the pool you want to mirror images in. In these examples, data is the name of the pool.
```
ceph_rbd_mirror_configure: true
ceph_rbd_mirror_pool: "data"
```
7. By default, ceph-ansible configures mirroring using pool mode which mirrors all images in a pool. Enable image mode where only images that have mirroring explicitly enabled are mirrored. To enable image mode, set ceph_rbd_mirror_mode to image:
```
ceph_rbd_mirror_mode: image
```
8. On the Ansible administration node, set a name for the cluster that rbd-mirror in the group_vars/rbdmirrors.yml file. Following the examples, the other cluster is named site-b.
```
ceph_rbd_mirror_remote_cluster: "site-b"
```
9. On the Ansible administration node, set the user name of the key using ceph_rbd_mirror_remote_user in group_vars/rbdmirrors.yml file. In these examples the user is named client.site-b.
```
ceph_rbd_mirror_remote_user: "client.site-b"
```
10. As the Ansible user on the administration node, run the Ansible playbook:
  - Bare-metal deployments:
    [user@admin ceph-ansible]$ ansible-playbook site.yml --limit rbdmirrors -i hosts
  - Container deployments:
    [user@admin ceph-ansible]$ ansible-playbook site-container.yml --limit rbdmirrors -i hosts
Explicitly enable mirroring on the desired images in both site-a and site-b clusters:
Syntax
Journal-based mirroring:
```
rbd mirror image enable POOL/IMAGE
```
Snapshot-based mirroring:
```
rbd mirror image enable POOL/IMAGE snapshot
```
Example
```
[root@mon ~]# rbd mirror image enable data/image1
[root@mon ~]# rbd mirror image enable data/image1 snapshot
```
Note
Repeat this step whenever you want to mirror new image to peer cluster.

Verify the mirroring status. Run the following command from the client node on the site-a cluster:

Example

Journal-based mirroring:

[root@mon ~]# rbd mirror image status data/image1
image1:
  global_id:   08027096-d267-47f8-b52e-59de1353a034
  state:       up+stopped 1
  description: local image is primary
  last_update: 2021-04-16 15:45:31

Snapshot-based mirroring:

[root@mon ~]# rbd mirror image status data/image1
image1:
  global_id:   47fd1aae-5f19-4193-a5df-562b5c644ea7
  state:       up+stopped 1
  description: local image is primary
  service:     admin on ceph-rbd1-vasi-43-5hwia4-node2
  last_update: 2022-01-20 12:42:54
  peer_sites:
    name: rbd-mirror.site-b
    state: up+replaying
    description: replaying, {"bytes_per_second":0.0,"bytes_per_snapshot":0.0,"local_snapshot_timestamp":1642693094,"remote_snapshot_timestamp":1642693094,"replay_state":"idle"}
    last_update: 2022-01-20 12:42:59
  snapshots:
    5 .mirror.primary.47fd1aae-5f19-4193-a5df-562b5c644ea7.dda146c6-5f21-4e75-ba93-660f6e57e301 (peer_uuids:[bfd09289-c9c9-40c8-b2d3-ead9b6a99a45])

1 1: The images should be in state up+stopped. Here, up means the rbd-mirror daemon is running and stopped means the image is not a target for replication from another cluster. This is because the images are primary on this cluster.

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

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

Note

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

Note

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

Prerequisites

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

Procedure

Install the rbd-mirror package on the client node connected to the site-b storage cluster:
Red Hat Enterprise Linux 7
```
[root@rbd-client ~]# yum install rbd-mirror
```
Red Hat Enterprise Linux 8
```
[root@rbd-client ~]# dnf install rbd-mirror
```
Note
The package is provided by the Red Hat Ceph Storage Tools repository.

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

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

Syntax

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

Example

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

For existing images, use the rbd feature enable command:

Syntax

rbd feature enable POOL_NAME/IMAGE_NAME FEATURE [,FEATURE]

Example

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

To enable exclusive-lock and journaling on all new images by default, add the following setting to the Ceph configuration file:
```
rbd_default_features = 125
```

Choose the mirroring mode, either pool or image mode.
Important
Use image mode for snapshot-based mirroring.
1. Enabling pool mode:
  Syntax
```
rbd mirror pool enable POOL_NAME MODE
```
  Example
```
[root@rbd-client ~]# rbd mirror pool enable data pool
```
  This example enables mirroring of the whole pool named data.
2. Enabling image mode:
  Syntax
```
rbd mirror pool enable POOL_NAME MODE
```
  Example
```
[root@rbd-client ~]# rbd mirror pool enable data image
```
  This example enables image mode mirroring on the pool named data.
3. Verify that mirroring has been successfully enabled:
  Syntax
```
rbd mirror pool info POOL_NAME
```
  Example
```
[root@rbd-client ~]# rbd mirror pool info data
Mode: image
Site Name: 94cbd9ca-7f9a-441a-ad4b-52a33f9b7148

Peer Sites: none
```

In the site-a cluster, complete the following steps:

On the Ceph client node, create a user:

Syntax

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

Example

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

Copy keyring to site-b cluster:

Syntax

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

Example

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

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

Syntax

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

Example

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

Note

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

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

Syntax

scp PATH_TO_BOOTSTRAP_TOKEN root@SECONDARY_CLUSTER:/root/

Example

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

In the site-b cluster, complete the following steps:

On the client node, create a user:

Syntax

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

Example

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

Copy keyring to the site-a cluster, the Ceph client node:

Syntax

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

Example

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

Import the bootstrap token:

Syntax

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

Example

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

Note

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

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

Syntax

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

Replace CLIENT_ID with the Ceph user created earlier.

Example

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

Important

Each rbd-mirror daemon must have a unique Client ID.

To verify the mirroring status, run the following command from a Ceph Monitor node in the site-a and site-b clusters:

Syntax

rbd mirror image status POOL_NAME/IMAGE_NAME

Example

Journal-based mirroring:

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

Snapshot-based mirroring:

[root@mon-site-a ~]# rbd mirror image status data/image1
image1:
  global_id:   47fd1aae-5f19-4193-a5df-562b5c644ea7
  state:       up+stopped 1
  description: local image is primary
  service:     admin on ceph-rbd1-vasi-43-5hwia4-node2
  last_update: 2022-01-20 12:42:54
  peer_sites:
    name: rbd-mirror.site-b
    state: up+replaying
    description: replaying, {"bytes_per_second":0.0,"bytes_per_snapshot":0.0,"local_snapshot_timestamp":1642693094,"remote_snapshot_timestamp":1642693094,"replay_state":"idle"}
    last_update: 2022-01-20 12:42:59
  snapshots:
    5 .mirror.primary.47fd1aae-5f19-4193-a5df-562b5c644ea7.dda146c6-5f21-4e75-ba93-660f6e57e301 (peer_uuids:[bfd09289-c9c9-40c8-b2d3-ead9b6a99a45])

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

Example

Journal-based mirroring:

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

Snapshot-based mirroring:

[root@mon-site-b ~]# rbd mirror image status data/image1
image1:
  global_id:   06acc9e6-a63d-4aa1-bd0d-4f3a79b0ae33
  state:       up+replaying 1
  description: replaying, {"bytes_per_second":0.0,"bytes_per_snapshot":0.0,"local_snapshot_timestamp":1642689843,"remote_snapshot_timestamp":1642689843,"replay_state":"idle"}
  service:     admin on ceph-rbd2-vasi-43-5hwia4-node2
  last_update: 2022-01-20 12:41:57

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

Note

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

Additional Resources

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

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

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

Note

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

Note

Prerequisites

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

Procedure

Install the rbd-mirror package on the client node connected to the site-a storage cluster, and the client node connected to the site-b storage cluster:
Red Hat Enterprise Linux 7
```
[root@rbd-client ~]# yum install rbd-mirror
```
Red Hat Enterprise Linux 8
```
[root@rbd-client ~]# dnf install rbd-mirror
```
Note
The package is provided by the Red Hat Ceph Storage Tools repository.

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

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

Syntax

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

Example

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

For existing images, use the rbd feature enable command:

Syntax

rbd feature enable POOL_NAME/IMAGE_NAME FEATURE [,FEATURE]

Example

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

To enable exclusive-lock and journaling on all new images by default, add the following setting to the Ceph configuration file:
```
rbd_default_features = 125
```

Choose the mirroring mode, either pool or image mode.
Important
Use image mode for snapshot-based mirroring.
1. Enabling pool mode:
  Syntax
```
rbd mirror pool enable POOL_NAME MODE
```
  Example
```
[root@rbd-client ~]# rbd mirror pool enable data pool
```
  This example enables mirroring of the whole pool named data.
2. Enabling image mode:
  Syntax
```
rbd mirror pool enable POOL_NAME MODE
```
  Example
```
[root@rbd-client ~]# rbd mirror pool enable data image
```
  This example enables image mode mirroring on the pool named data.
3. Verify that mirroring has been successfully enabled:
  Syntax
```
rbd mirror pool info POOL_NAME
```
  Example
```
[root@rbd-client ~]# rbd mirror pool info data
Mode: image
Site Name: 94cbd9ca-7f9a-441a-ad4b-52a33f9b7148

Peer Sites: none
```

In the site-a cluster, complete the following steps:

On the Ceph client node, create a user:

Syntax

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

Example

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

Copy keyring to site-b cluster:

Syntax

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

Example

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

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

Syntax

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

Example

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

Note

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

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

Syntax

scp PATH_TO_BOOTSTRAP_TOKEN root@SECONDARY_CLUSTER:/root/

Example

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

In the site-b cluster, complete the following steps:

On the client node, create a user:

Syntax

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

Example

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

Copy keyring to the site-a cluster, the Ceph client node:

Syntax

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

Example

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

Import the bootstrap token:

Syntax

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

Example

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

Note

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

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

Syntax

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

Replace CLIENT_ID with the Ceph user created earlier.

Example

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

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

Example

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

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

Important

Each rbd-mirror daemon must have a unique Client ID.

To verify the mirroring status, run the following command from a Ceph Monitor node in the site-a and site-b clusters:

Syntax

rbd mirror image status POOL_NAME/IMAGE_NAME

Example

Journal-based mirroring:

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

Snapshot-based mirroring:

[root@mon-site-a ~]# rbd mirror image status data/image1
image1:
  global_id:   47fd1aae-5f19-4193-a5df-562b5c644ea7
  state:       up+stopped 1
  description: local image is primary
  service:     admin on ceph-rbd1-vasi-43-5hwia4-node2
  last_update: 2022-01-20 12:42:54
  peer_sites:
    name: rbd-mirror.site-b
    state: up+replaying
    description: replaying, {"bytes_per_second":0.0,"bytes_per_snapshot":0.0,"local_snapshot_timestamp":1642693094,"remote_snapshot_timestamp":1642693094,"replay_state":"idle"}
    last_update: 2022-01-20 12:42:59
  snapshots:
    5 .mirror.primary.47fd1aae-5f19-4193-a5df-562b5c644ea7.dda146c6-5f21-4e75-ba93-660f6e57e301 (peer_uuids:[bfd09289-c9c9-40c8-b2d3-ead9b6a99a45])

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

Example

Journal-based mirroring:

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

Snapshot-based mirroring:

[root@mon-site-b ~]# rbd mirror image status data/image1
image1:
  global_id:   06acc9e6-a63d-4aa1-bd0d-4f3a79b0ae33
  state:       up+replaying 1
  description: replaying, {"bytes_per_second":0.0,"bytes_per_snapshot":0.0,"local_snapshot_timestamp":1642689843,"remote_snapshot_timestamp":1642689843,"replay_state":"idle"}
  service:     admin on ceph-rbd2-vasi-43-5hwia4-node2
  last_update: 2022-01-20 12:41:57

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

Note

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

Additional Resources

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

5.7. Administration for mirroring Ceph block devices

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

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

5.7.1. Prerequisites

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

5.7.2. Viewing information about peers

View information about storage cluster peers.

Prerequisites

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

Procedure

To view information about the peers:

Syntax

rbd mirror pool info POOL_NAME

Example

[root@rbd-client ~]# rbd mirror pool info data
Mode: pool
Site Name: site-a

Peer Sites:

UUID: 950ddadf-f995-47b7-9416-b9bb233f66e3
Name: site-b
Mirror UUID: 4696cd9d-1466-4f98-a97a-3748b6b722b3
Direction: rx-tx
Client: client.site-b

5.7.3. Enabling mirroring on a pool

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

Prerequisites

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

Procedure

To enable mirroring on a pool:
Syntax
```
rbd mirror pool enable POOL_NAME MODE
```
Example
```
[root@rbd-client ~]# rbd mirror pool enable data pool
```
This example enables mirroring of the whole pool named data.
Example
```
[root@rbd-client ~]# rbd mirror pool enable data image
```
This example enables image mode mirroring on the pool named data.

Additional Resources

See the Mirroring Ceph block devices section in the Red Hat Ceph Storage Block Device Guide for details.

5.7.4. Disabling mirroring on a pool

Before disabling mirroring, remove the peer clusters.

Note

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

Prerequisites

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

Procedure

To disable mirroring on a pool:
Syntax
```
rbd mirror pool disable POOL_NAME
```
Example
```
[root@rbd-client ~]# rbd mirror pool disable data
```
This example disables mirroring of a pool named data.

Additional Resources

See the Configuring image one-way mirroring section in the Red Hat Ceph Storage Block Device Guide for details.
See the Removing a storage cluster peer section in the Red Hat Ceph Storage Block Device Guide for details.

5.7.5. Enabling image mirroring

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

Prerequisites

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

Procedure

Enable mirroring for a specific image within the pool:
Syntax
```
rbd mirror image enable POOL_NAME/IMAGE_NAME
```
Example
```
[root@rbd-client ~]# rbd mirror image enable data/image2
```
This example enables mirroring for the image2 image in the data pool.

Additional Resources

See the Enabling mirroring on a pool section in the Red Hat Ceph Storage Block Device Guide for details.

5.7.6. Disabling image mirroring

Disable the mirror for images.

Prerequisites

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

Procedure

To disable mirroring for a specific image:
Syntax
```
rbd mirror image disable POOL_NAME/IMAGE_NAME
```
Example
```
[root@rbd-client ~]# rbd mirror image disable data/image2
```
This example disables mirroring of the image2 image in the data pool.

5.7.7. Image promotion and demotion

Promote or demote an image.

Note

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

Prerequisites

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

Procedure

To demote an image to non-primary:

Syntax

rbd mirror image demote POOL_NAME/IMAGE_NAME

Example

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

This example demotes the image2 image in the data pool.

To promote an image to primary:
Syntax
```
rbd mirror image promote POOL_NAME/IMAGE_NAME
```
Example
```
[root@rbd-client ~]# rbd mirror image promote data/image2
```
This example promotes image2 in the data pool.
Depending on which type of mirroring you are using, see either Recovering from a disaster with one-way mirroring or Recovering from a disaster with two-way mirroring for details.
Use the --force option to force promote a non-primary image:
Syntax
```
rbd mirror image promote --force POOL_NAME/IMAGE_NAME
```
Example
```
[root@rbd-client ~]# rbd mirror image promote --force data/image2
```
Use forced promotion when the demotion cannot be propagated to the peer Ceph storage cluster. For example, because of cluster failure or communication outage.

Additional Resources

See the Failover after a non-orderly shutdown section in the Red Hat Ceph Storage Block Device Guide for details.

5.7.8. Image resynchronization

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

Prerequisites

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

Procedure

To request a resynchronization to the primary image:
Syntax
```
rbd mirror image resync POOL_NAME/IMAGE_NAME
```
Example
```
[root@rbd-client ~]# rbd mirror image resync data/image2
```
This example requests resynchronization of image2 in the data pool.

Additional Resources

To recover from an inconsistent state because of a disaster, see either Recovering from a disaster with one-way mirroring or Recovering from a disaster with two-way mirroring for details.

5.7.9. Adding a storage cluster peer

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

Prerequisites

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

Procedure

Syntax

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

Example

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

5.7.10. Removing a storage cluster peer

Remove a storage cluster peer by specifying the peer UUID.

Prerequisites

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

Procedure

Specify the pool name and the peer Universally Unique Identifier (UUID).
Syntax
```
rbd mirror pool peer remove POOL_NAME PEER_UUID
```
Example
```
[root@rbd-client ~]# rbd mirror pool peer remove data 7e90b4ce-e36d-4f07-8cbc-42050896825d
```
Tip
To view the peer UUID, use the rbd mirror pool info command.

5.7.11. Getting mirroring status for a pool

Get the mirror status for a pool.

Prerequisites

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

Procedure

To get the mirroring pool summary:
Syntax
```
rbd mirror pool status POOL_NAME
```
Example
```
[root@rbd-client ~]# rbd mirror pool status data
health: OK
images: 1 total
```
Tip
To output status details for every mirroring image in a pool, use the --verbose option.

5.7.12. Getting mirroring status for a single image

Get the mirror status for an image.

Prerequisites

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

Procedure

To get the status of a mirrored image:

Syntax

rbd mirror image status POOL_NAME/IMAGE_NAME

Example

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

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

5.7.13. Delaying block device replication

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

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

Prerequisites

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

Procedure

To utilize delayed replication for a specific image, on the primary image, run the following rbd CLI command:
Syntax
```
rbd image-meta set POOL_NAME/IMAGE_NAME conf_rbd_mirroring_replay_delay MINIMUM_DELAY_IN_SECONDS
```
Example
```
[root@rbd-client ~]# rbd image-meta set vms/vm-1 conf_rbd_mirroring_replay_delay 600
```
This example sets a 10 minute minimum replication delay on image vm-1 in the vms pool.

5.7.14. Asynchronous updates and Ceph block device mirroring

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

Note

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

5.7.15. Creating an image mirror-snapshot

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

Prerequisites

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

Important

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

Procedure

To create an image-mirror snapshot:

Syntax

rbd --cluster CLUSTER_NAME mirror image snapshot POOL_NAME/IMAGE_NAME

Example

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

Additional Resources

See the Mirroring Ceph block devices section in the Red Hat Ceph Storage Block Device Guide for details.

5.7.16. Scheduling mirror-snapshots

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

Additional Resources

See the Mirroring Ceph block devices section in the Red Hat Ceph Storage Block Device Guide for details.

5.7.17. Creating a mirror-snapshot schedule

Create a mirror-snapshot schedule.

Prerequisites

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

Procedure

To create a mirror-snapshot schedule:

Syntax

rbd mirror snapshot schedule add --pool POOL_NAME --image IMAGE_NAME INTERVAL START_TIME

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

Example

Scheduling at image level:

[root@rbd-client ~]# rbd mirror snapshot schedule add --pool data --image image1 6h

Scheduling at pool level:

[root@rbd-client ~]# rbd mirror snapshot schedule add --pool data 24h 14:00:00-05:00

Scheduling at global level:

[root@rbd-client ~]# rbd mirror snapshot schedule add 48h

Additional Resources

See the Mirroring Ceph block devices section in the Red Hat Ceph Storage Block Device Guide for details.

5.7.18. Listing all snapshot schedules at a specific level

List all snapshot schedules at a specific level.

Prerequisites

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

Procedure

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

Syntax

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

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

Example

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

Additional Resources

See the Mirroring Ceph block devices section in the Red Hat Ceph Storage Block Device Guide for details.

5.7.19. Removing a mirror-snapshot schedule

Remove a mirror-snapshot schedule.

Prerequisites

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

Procedure

To remove a mirror-snapshot schedule:

Syntax

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

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

Example

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

Example

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

Additional Resources

See the Mirroring Ceph block devices section in the Red Hat Ceph Storage Block Device Guide for details.

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

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

Prerequisites

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

Procedure

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

Syntax

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

Example

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

Additional Resources

See the Mirroring Ceph block devices section in the Red Hat Ceph Storage Block Device Guide for details.

5.8. Recover from a disaster

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

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

5.8.1. Prerequisites

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

5.8.2. Disaster recovery

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

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

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

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

Additional Resources

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

5.8.3. Recover from a disaster with one-way mirroring

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

Important

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

5.8.4. Recover from a disaster with two-way mirroring

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

Additional Resources

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

5.8.5. Failover after an orderly shutdown

Failover to the secondary storage cluster after an orderly shutdown.

Prerequisites

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

Procedure

Stop all clients that use the primary image. This step depends on which clients use the image. For example, detach volumes from any OpenStack instances that use the image.

Demote the primary images located on the site-a cluster by running the following commands on a monitor node in the site-a cluster:

Syntax

rbd mirror image demote POOL_NAME/IMAGE_NAME

Example

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

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

Syntax

rbd mirror image promote POOL_NAME/IMAGE_NAME

Example

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

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

[root@rbd-client ~]# rbd mirror image status data/image1
image1:
  global_id:   08027096-d267-47f8-b52e-59de1353a034
  state:       up+stopped
  description: local image is primary
  last_update: 2019-04-17 16:04:37
[root@rbd-client ~]# rbd mirror image status data/image2
image2:
  global_id:   596f41bc-874b-4cd4-aefe-4929578cc834
  state:       up+stopped
  description: local image is primary
  last_update: 2019-04-17 16:04:37

Resume the access to the images. This step depends on which clients use the image.

Additional Resources

See the Block Storage and Volumes chapter in the Red Hat OpenStack Platform Storage Guide.

5.8.6. Failover after a non-orderly shutdown

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

Prerequisites

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

Procedure

Verify that the primary storage cluster is down.
Stop all clients that use the primary image. This step depends on which clients use the image. For example, detach volumes from any OpenStack instances that use the image.
Promote the non-primary images from a Ceph Monitor node in the site-b storage cluster. Use the --force option, because the demotion cannot be propagated to the site-a storage cluster:
Syntax
```
rbd mirror image promote --force POOL_NAME/IMAGE_NAME
```
Example
```
[root@rbd-client ~]# rbd mirror image promote --force data/image1
[root@rbd-client ~]# rbd mirror image promote --force data/image2
```

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

Example

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

Additional Resources

See the Block Storage and Volumes chapter in the Red Hat OpenStack Platform Storage Guide.

5.8.7. Prepare for fail back

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

Prerequisites

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

Procedure

On the client node of the site-a storage cluster, install the rbd-mirror package:
```
[root@rbd-client ~]# yum install rbd-mirror
```
Note
The package is provided by the Red Hat Ceph Storage Tools repository.
On the client node of the site-a storage cluster, specify the storage cluster name by adding the CLUSTER option to the /etc/sysconfig/ceph file:
```
CLUSTER=site-b
```
Copy the site-b Ceph configuration file and keyring file from the site-b Ceph Monitor node to the site-a Ceph Monitor and client nodes:
Syntax
```
scp /etc/ceph/ceph.conf USER@SITE_A_MON_NODE_NAME:/etc/ceph/site-b.conf
scp /etc/ceph/site-b.client.site-b.keyring root@SITE_A_MON_NODE_NAME:/etc/ceph/
scp /etc/ceph/ceph.conf user@SITE_A_CLIENT_NODE_NAME:/etc/ceph/site-b.conf
scp /etc/ceph/site-b.client.site-b.keyring user@SITE_A_CLIENT_NODE_NAME:/etc/ceph/
```
Note
The scp commands that transfer the Ceph configuration file from the site-b Ceph Monitor node to the site-a Ceph Monitor and client nodes renames the file to site-a.conf. The keyring file name stays the same.
Copy the site-a keyring file from the site-a Ceph Monitor node to the site-a client node:
Syntax
```
scp /etc/ceph/site-a.client.site-a.keyring <user>@SITE_A_CLIENT_HOST_NAME:/etc/ceph/
```

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

Syntax

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

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

Example

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

From the client node on the site-a cluster, add the site-b cluster as a peer:
Example
```
[root@rbd-client ~]# rbd --cluster site-a mirror pool peer add data client.site-b@site-b -n client.site-a
```
If you are using multiple secondary storage clusters, only the secondary storage cluster chosen to fail over to, and fail back from, must be added.

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

Syntax

rbd mirror pool info POOL_NAME

Example

[root@rbd-client ~]# rbd mirror pool info data
Mode: image
Site Name: site-a

Peer Sites:

UUID: 950ddadf-f995-47b7-9416-b9bb233f66e3
Name: site-b
Mirror UUID: 4696cd9d-1466-4f98-a97a-3748b6b722b3
Direction: rx-tx
Client: client.site-b

Additional Resources

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

5.8.7.1. Fail back to the primary storage cluster

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

Prerequisites

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

Procedure

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

Example

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

From a Ceph Monitor node on the site-a storage cluster determine if the images are still primary:
Syntax
```
rbd info POOL_NAME/IMAGE_NAME
```
Example
```
[root@rbd-client ~]# rbd info data/image1
[root@rbd-client ~]# rbd info data/image2
```
In the output from the commands, look for mirroring primary: true or mirroring primary: false, to determine the state.
Demote any images that are listed as primary by running a command like the following from a Ceph Monitor node in the site-a storage cluster:
Syntax
```
rbd mirror image demote POOL_NAME/IMAGE_NAME
```
Example
```
[root@rbd-client ~]# rbd mirror image demote data/image1
```

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

Syntax

rbd mirror image resync POOL_NAME/IMAGE_NAME

Example

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

After some time, ensure resynchronization of the images is complete by verifying they are in the up+replaying state. Check their state by running the following commands on a monitor node in the site-a storage cluster:
Syntax
```
rbd mirror image status POOL_NAME/IMAGE_NAME
```
Example
```
[root@rbd-client ~]# rbd mirror image status data/image1
[root@rbd-client ~]# rbd mirror image status data/image2
```
Demote the images on the site-b storage cluster by running the following commands on a Ceph Monitor node in the site-b storage cluster:
Syntax
```
rbd mirror image demote POOL_NAME/IMAGE_NAME
```
Example
```
[root@rbd-client ~]# rbd mirror image demote data/image1
[root@rbd-client ~]# rbd mirror image demote data/image2
```
Note
If there are multiple secondary storage clusters, this only needs to be done from the secondary storage cluster where it was promoted.
Promote the formerly primary images located on the site-a storage cluster by running the following commands on a Ceph Monitor node in the site-a storage cluster:
Syntax
```
rbd mirror image promote POOL_NAME/IMAGE_NAME
```
Example
```
[root@rbd-client ~]# rbd mirror image promote data/image1
[root@rbd-client ~]# rbd mirror image promote data/image2
```

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

Syntax

rbd mirror image status POOL_NAME/IMAGE_NAME

Example

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

5.8.8. Remove two-way mirroring

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

Prerequisites

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

Procedure

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

Example

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

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

Syntax

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

Example

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

Language and Page Formatting Options

Chapter 5. Mirroring Ceph block devices

5.1. Prerequisites

5.2. Ceph block device mirroring

5.3. Configuring one-way mirroring using Ansible

5.4. Configuring two-way mirroring using Ansible

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

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

5.7. Administration for mirroring Ceph block devices

5.7.1. Prerequisites

5.7.2. Viewing information about peers

5.7.3. Enabling mirroring on a pool

5.7.4. Disabling mirroring on a pool

5.7.5. Enabling image mirroring

5.7.6. Disabling image mirroring

5.7.7. Image promotion and demotion

5.7.8. Image resynchronization

5.7.9. Adding a storage cluster peer

5.7.10. Removing a storage cluster peer

5.7.11. Getting mirroring status for a pool

5.7.12. Getting mirroring status for a single image

5.7.13. Delaying block device replication

5.7.14. Asynchronous updates and Ceph block device mirroring

5.7.15. Creating an image mirror-snapshot

5.7.16. Scheduling mirror-snapshots

5.7.17. Creating a mirror-snapshot schedule

5.7.18. Listing all snapshot schedules at a specific level

5.7.19. Removing a mirror-snapshot schedule

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

5.8. Recover from a disaster

5.8.1. Prerequisites

5.8.2. Disaster recovery

5.8.3. Recover from a disaster with one-way mirroring

5.8.4. Recover from a disaster with two-way mirroring

5.8.5. Failover after an orderly shutdown

5.8.6. Failover after a non-orderly shutdown

5.8.7. Prepare for fail back

5.8.7.1. Fail back to the primary storage cluster

5.8.8. Remove two-way mirroring

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