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Alternate_Storage_Pools.md

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Alternate Storage Pools

Description

Creating, maintaining, and removing Ceph storage pools.

Use cases

  • A landing space for the CSM tarball used for upgrades.
  • Temporary space needed for maintenance or pre/post upgrade activities.

Best practices

  • Apply a proper quota to any pools created.
    • This will use storage from the default crush rule which is utilizing every OSD.
    • Improper use of this procedure can have a negative impact on the cluster and space available to running services.
      • Failure to set a quota and not policing space usage can result in the Ceph cluster going into read-only mode.
        • This will cause running services to crash if the space issue is not resolved quickly.
  • Cleanup after the criteria for the pool creation has been met.
    • This can be as simple as removing volumes but leaving the pool for future use.

Procedures

This example shows the creation and mounting of an rbd device on ncn-m001.

NOTE: The commands to create and delete pools or rbd devices must be run from a master node or one of the first three storage nodes (ncn-s001, ncn-s002, or ncn-s003).

Create a storage pool

The below example will create a storage pool name csm-release. The pool name can be changed to better reflect any use cases outside of support for upgrades. The 3 3 arguments can be left unchanged. For more information on their meaning and possible alternative values, see the Ceph product documentation.

ceph osd pool create csm-release 3 3
ceph osd pool application enable csm-release rbd
ceph osd pool set-quota csm-release max_bytes 500G
ceph osd pool get-quota csm-release

Output:

ncn-s001:~ # ceph osd pool create csm-release 3 3
pool 'csm-release' created

ncn-s001:~ # ceph osd pool application enable csm-release rbd
enabled application 'rbd' on pool 'csm-release'

ncn-s001:~ # ceph osd pool set-quota csm-release max_bytes 500G
set-quota max_bytes = 536870912000 for pool csm-release

ncn-s001:~ # ceph osd pool get-quota csm-release
quotas for pool 'csm-release':
  max objects: N/A
  max bytes  : 500 GiB  (current num bytes: 0 bytes)

NOTES:

  • The above example sets the quota to 500 GiB.
    • If this pool is fully utilized it will be using 1.5 TiB of raw space.
    • This space counts against the total space provided by the cluster; Use cautiously.
    • If this pool or any pool reaches 95-100% utilization, then all volumes for the fully utilized pool will go into read-only mode.

Create and map an rbd device

IMPORTANT:

  • Creating an rbd device requires proper access and must be run from a master node or one of the first three storage nodes (ncn-s001, ncn-s002, or ncn-s003).
  • Mounting a device will occur on the node where the storage needs to be present.
rbd create -p csm-release release_version --size 100G
rbd map -p csm-release release_version
rbd showmapped

Output:

ncn-m001:~ # rbd create -p csm-release release_version --size 100G

ncn-m001:~ # rbd map -p csm-release release_version
/dev/rbd0

ncn-m001:~ # rbd showmapped
id  pool         namespace  image            snap  device
0   csm-release             release_version  -     /dev/rbd0

IMPORTANT NOTE:

  • Master nodes normally do not have rbd devices mapped via Ceph provisioner.
    • If mapping to a worker node where there are mapped PVCs, then ensure the proper rbd device is being captured for the following steps.
    • Failure to do this most likely will result in data corruption or loss.

Mount an rbd device

mkfs.ext4 /dev/rbd0
mkdir -pv /etc/cray/csm/csm-release
mount /dev/rbd0 /etc/cray/csm/csm-release/
mountpoint /etc/cray/csm/csm-release/

Output:

ncn-m001:~ # mkfs.ext4 /dev/rbd0
mke2fs 1.43.8 (1-Jan-2018)
Discarding device blocks: done
Creating filesystem with 26214400 4k blocks and 6553600 inodes
Filesystem UUID: d5fe6df4-a0ab-49bc-8d49-9cc62700915d
Superblock backups stored on blocks:
 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
 4096000, 7962624, 11239424, 20480000, 23887872

Allocating group tables: done
Writing inode tables: done
Creating journal (131072 blocks): done
Writing superblocks and filesystem accounting information: mkdir done

ncn-m001:~ # mkdir -pv /etc/cray/csm/csm-release
mkdir: created directory '/etc/cray/csm'
mkdir: created directory '/etc/cray/csm/csm-release'

Note that the below command does not return output on success:

ncn-m001:~ # mount /dev/rbd0 /etc/cray/csm/csm-release/

ncn-m001:~ # mountpoint /etc/cray/csm/csm-release/
/etc/cray/csm/csm-release/ is a mountpoint

Move an rbd device to another node

On node where the rbd device is mapped:

umount /etc/cray/csm/csm-release
rbd unmap  -p csm-release release_version
rbd showmapped

NOTE: There should be no output from the above unless other rbd devices are mapped on the node. In this case, it is a master node, which typically will not have mapped rbd devices.

Then run the following commands on the destination node (that is, the node where the rbd device is being remapped to).

rbd map -p csm-release release_version
rbd showmapped
mkdir -pv /etc/cray/csm/csm-release 
mount /dev/rbd0 /etc/cray/csm/csm-release

Output:

ncn-m002:~ # rbd map -p csm-release release_version
/dev/rbd0

The following output will vary based on the existence of the directories.

ncn-m002:~ # mkdir -pv /etc/cray/csm/csm-release
mkdir: created directory '/etc/cray'
mkdir: created directory '/etc/cray/csm'
mkdir: created directory '/etc/cray/csm/csm-release'

ncn-m002:~ # rbd showmapped
id  pool         namespace  image            snap  device
0   csm-release             release_version  -     /dev/rbd0

ncn-m002:~ # mount /dev/rbd0 /etc/cray/csm/csm-release/

Unmount, unmap, and delete an rbd device

umount /etc/cray/csm/csm-release
rbd unmap /dev/rbd0
rbd showmapped
rbd remove csm-release/release_version

Output:

ncn-m001:~ # umount /etc/cray/csm/csm-release
ncn-m001:~ # rbd unmap /dev/rbd0
ncn-m001:~ # rbd showmapped
ncn-m001:~ # rbd remove csm-release/release_version
Removing image: 100% complete...done.

Remove a storage pool

CRITICAL NOTE: This will permanently delete data.

  1. Check to see if the cluster is allowing pool deletion.

    ceph config get mon mon_allow_pool_delete

    Output:

    ncn-s001:~ # ceph config get mon mon_allow_pool_delete
true

    If the above command shows false, then enable it using the following command:

    ceph config set mon mon_allow_pool_delete true

  2. Remove the pool.

    ceph osd pool rm csm-release csm-release --yes-i-really-really-mean-it

    Output:

    ncn-s001:~ # ceph osd pool rm csm-release csm-release --yes-i-really-really-mean-it
pool 'csm-release' removed