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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
# gluster volume geo-replication MASTER_VOL SLAVE_HOST::SLAVE_VOL pauseCopy to Clipboard Copied! Toggle word wrap Toggle overflow For example,gluster volume geo-replication master-vol example.com::slave-vol pause
# gluster volume geo-replication master-vol example.com::slave-vol pause Pausing geo-replication session between master-vol example.com::slave-vol has been successfulCopy to Clipboard Copied! Toggle word wrap Toggle overflow 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]
# 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- Snapshot creation will fail if any brick is down. In a n-way replicated Red Hat Gluster Storage volume where n >= 3 snapshot is allowed even if some of the bricks are down. In such case quorum is checked. Quorum is checked only when theforceoption is provided, else by-default the snapshot create will fail if any brick is down. Refer the Overview section for more details on quorum.- 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
# gluster snapshot create snap1 vol1 no-timestamp
snapshot create: success: Snap snap1 created successfully
For Example 2:
gluster snapshot create snap1 vol1
# 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
/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
# gluster volume geo-replication MASTER_VOL SLAVE_HOST::SLAVE_VOL resume
For example,
gluster volume geo-replication master-vol example.com::slave-vol resume
# 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.
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