Ceph backup driver¶
The Ceph backup driver backs up volumes of any type to a Ceph back-end store. The driver can also detect whether the volume to be backed up is a Ceph RBD volume, and if so, it tries to perform incremental and differential backups.
For source Ceph RBD volumes, you can perform backups within the same Ceph pool (not recommended). You can also perform backups between different Ceph pools and between different Ceph clusters.
At the time of writing, differential backup support in Ceph/librbd was quite new. This driver attempts a differential backup in the first instance. If the differential backup fails, the driver falls back to full backup/copy.
If incremental backups are used, multiple backups of the same volume are stored as snapshots so that minimal space is consumed in the backup store. It takes far less time to restore a volume than to take a full copy.
By default, all incremental backups are held on the source volume storage,
which can take up much disk space on the usually more expensive
primary storage compared to backup storage. Enabling the option
backup_ceph_max_snapshots can save disk space on the source
volume storage by only keeping a limited number of snapshots per backup volume.
After every successful creation of a new incremental backup, the Ceph backup
driver will then ensure that excess snapshots of the corresponding backup
volume are deleted so that only the backup_ceph_max_snapshots
most recent snapshots are kept on the primary storage.
However, this can cause incremental backups to automatically become full
backups instead if a user manually deleted at least
backup_ceph_max_snapshots incremental backups. In that case
the next snapshot, being a full backup, will require more disk space on
the backup storage and will take longer to complete than an incremental
backup would have.
Thus, the option allows to configure a tradeoff between required space on the source volume storage and required space on the backup storage as well as a longer backup process under the above conditions.
Note
Block Storage enables you to:
Restore to a new volume, which is the default and recommended action.
Restore to the original volume from which the backup was taken. The restore action takes a full copy because this is the safest action.
To enable the Ceph backup driver, include the following option in the
cinder.conf file:
backup_driver = cinder.backup.drivers.ceph.CephBackupDriver
The following configuration options are available for the Ceph backup driver.
Configuration option = Default value |
Description |
|---|---|
|
(Integer) The chunk size, in bytes, that a backup is broken into before transfer to the Ceph object store. |
|
(String) Ceph configuration file to use. |
|
(Boolean) If True, apply JOURNALING and EXCLUSIVE_LOCK feature bits to the backup RBD objects to allow mirroring |
|
(Integer) Number of the most recent snapshots to keep. 0 indicates to keep an unlimited number of snapshots. Configuring this option can save disk space by only keeping a limited number of snapshots on the source volume storage. However, if a user deletes all incremental backups which still have snapshots on the source storage, the next incremental backup will automatically become a full backup as no common snapshot exists anymore. |
|
(String) The Ceph pool where volume backups are stored. |
|
(Integer) RBD stripe count to use when creating a backup image. |
|
(Integer) RBD stripe unit to use when creating a backup image. |
|
(String) The Ceph user to connect with. Default here is to use the same user as for Cinder volumes. If not using cephx this should be set to None. |
|
(Boolean) If True, always discard excess bytes when restoring volumes i.e. pad with zeroes. |
This example shows the default options for the Ceph backup driver.
backup_ceph_conf=/etc/ceph/ceph.conf
backup_ceph_user = cinder-backup
backup_ceph_chunk_size = 134217728
backup_ceph_pool = backups
backup_ceph_stripe_unit = 0
backup_ceph_stripe_count = 0
backup_ceph_max_snapshots = 0
