Migrating a pool

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Sometimes it is necessary to migrate all objects from one pool to another. This is done in cases such as needing to change parameters that cannot be modified on a specific pool. For example, needing to reduce the number of placement groups of a pool.

About this task

Important: When a workload is using only Ceph Block Device images, use the following procedures:
The migration methods described for Ceph Block Device are more recommended than those documented here. using the cppool does not preserve all snapshots and snapshot related metadata, resulting in an unfaithful copy of the data. For example, copying an RBD pool does not completely copy the image. In this case, snaps are not present and will not work properly. The cppool also does not preserve the user_version field that some librados users may rely on.

If migrating a pool is necessary and your user workloads contain images other than Ceph Block Devices, continue with one of the procedures documented here.

Before you begin

  • If using the rados cppool command:
    • Read-only access to the pool is required.
    • Only use this command if you do not have RBD images and its snaps and user_version consumed by librados.
  • If using the local drive RADOS commands, verify that sufficient cluster space is available. Two, three, or more copies of data will be present as per pool replication factor.

Migrating directly

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Copy all objects with the rados cppool command.
Important: Read-only access to the pool is required during copy.
ceph osd pool create NEW_POOL PG_NUM [ <other new pool parameters> ]
rados cppool SOURCE_POOL NEW_POOL
ceph osd pool rename SOURCE_POOL NEW_SOURCE_POOL_NAME
ceph osd pool rename NEW_POOL SOURCE_POOL
For example,
[ceph: root@host01 /]# ceph osd pool create pool1 250
[ceph: root@host01 /]# rados cppool pool2 pool1
[ceph: root@host01 /]# ceph osd pool rename pool2 pool3
[ceph: root@host01 /]# ceph osd pool rename pool1 pool2

Migrating through a local drive

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Procedure

  1. Use the rados export and rados import commands and a temporary local directory to save all exported data.
    ceph osd pool create NEW_POOL PG_NUM [ <other new pool parameters> ]
rados export --create SOURCE_POOL FILE_PATH
rados import FILE_PATH NEW_POOL
    For example,
    [ceph: root@host01 /]# ceph osd pool create pool1 250
[ceph: root@host01 /]# rados export --create pool2 <path of export file>
[ceph: root@host01 /]# rados import <path of export file> pool1
  2. Required: Stop all I/O to the source pool.
  3. Required: Resynchronize all modified objects.
    rados export --workers 5 SOURCE_POOL FILE_PATH
rados import --workers 5 FILE_PATH NEW_POOL
    For example,
    [ceph: root@host01 /]# rados export --workers 5 pool2 <path of export file>
[ceph: root@host01 /]# rados import --workers 5 <path of export file> pool1