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8.2. Creating Snapshots
Before creating a snapshot ensure that the following prerequisites are met:
- Red Hat Gluster Storage volume has to be present and the volume has to be in the
Startedstate. - All the bricks of the volume have to be on an independent thin logical volume(LV).
- Snapshot names must be unique in the cluster.
- All the bricks of the volume should be up and running, unless it is a n-way replication where n >= 3. In such case quorum must be met. For more information see Chapter 8, Managing Snapshots
- No other volume operation, like
rebalance,add-brick, etc, should be running on the volume. - Total number of snapshots in the volume should not be equal to Effective snap-max-hard-limit. For more information see Configuring Snapshot Behavior.
- If you have a geo-replication setup, then pause the geo-replication session if it is running, by executing the following command:
# gluster volume geo-replication MASTER_VOL SLAVE_HOST::SLAVE_VOL pause
For example,# gluster volume geo-replication master-vol example.com::slave-vol pause Pausing geo-replication session between master-vol example.com::slave-vol has been successful
Ensure that you take the snapshot of the master volume and then take snapshot of the slave volume.
To create a snapshot of the volume, run the following command:
# gluster snapshot create <snapname> <volname> [no-timestamp] [description <description>] [force]
where,
- snapname - Name of the snapshot that will be created.
- VOLNAME(S) - Name of the volume for which the snapshot will be created. We only support creating snapshot of single volume.
- description - This is an optional field that can be used to provide a description of the snap that will be saved along with the snap.
force- The behavior of snapshot creation command remains the same with and without the force option.- no-timestamp: By default a timestamp is appended to the snapshot name. If you do not want to append timestamp then pass no-timestamp as an argument.
Note
Snapshots are not activated on creation by default; to enable this behavior for all future snapshot creations, set the
activate-on-create parameter to enabled.
For Example 1:
# gluster snapshot create snap1 vol1 no-timestamp snapshot create: success: Snap snap1 created successfully
For Example 2:
# gluster snapshot create snap1 vol1 snapshot create: success: Snap snap1_GMT-2015.07.20-10.02.33 created successfully
Snapshot of a Red Hat Gluster Storage volume creates a read-only Red Hat Gluster Storage volume. This volume will have identical configuration as of the original / parent volume. Bricks of this newly created snapshot is mounted as
/var/run/gluster/snaps/<snap-volume-name>/brick<bricknumber>.
For example, a snapshot with snap volume name
0888649a92ea45db8c00a615dfc5ea35 and having two bricks will have the following two mount points:
/var/run/gluster/snaps/0888649a92ea45db8c00a615dfc5ea35/brick1 /var/run/gluster/snaps/0888649a92ea45db8c00a615dfc5ea35/brick2
These mounts can also be viewed using the
df or mount command.
Note
If you have a geo-replication setup, after creating the snapshot, resume the geo-replication session by running the following command:
# gluster volume geo-replication MASTER_VOL SLAVE_HOST::SLAVE_VOL resume
For example,
# gluster volume geo-replication master-vol example.com::slave-vol resume Resuming geo-replication session between master-vol example.com::slave-vol has been successful
Volume snapshot creation results in the creation of snapshot pool of blocks that contains a copy of the LVM metadata. After taking a snapshot, when new data is written to gluster volume, the snapshot pool is overwritten and the changes are copied to the main gluster volume. As a result, the snapshot pool consumes more metadata space if data changes after the snapshot is taken.
