Snapshots

Snapshots enable the saving of a filesystem state to a directory and can be used for backup, archiving and testing purposes.

Snapshots allow the saving of a filesystem state to a hidden .snapshots directory under the root filesystem. They can be used for:

• Physical backup: The snapshots directory can be copied into a different storage system, possibly on another site, using either the WEKA system Snap-To-Object feature or third-party software.

• Logical backup: Periodic snapshots enable filesystem restoration to a previous state if logical data corruption occurs.

• Archive: Periodic snapshots enable accessing a previous filesystem state for compliance or other needs.

• DevOps environments: Writable snapshots enable the execution of software tests on copies of the data.

Snapshots do not impact system performance and can be taken for each filesystem while applications run. They consume minimal space, according to the differences between the filesystem and the snapshots, or between the snapshots, in 4K granularity.

Snapshot space consumption is taken from the free space available in the filesystem. As snapshots grow due to changes in the filesystem, they continue to consume additional space.

If the filesystem reaches its free space limit, additional writes may be temporarily restricted until space is freed. In such cases, managing available storage—such as deleting older snapshots or optimizing storage usage—can help maintain smooth system operation.

You can retrieve the estimated reclaimable space using the command: weka fs snapshot. See Working with snapshots considerations.

You can create a writable snapshot. A writable snapshot cannot be changed to a read-only snapshot.

The WEKA system supports the following snapshot operations:

• View snapshots.

• Create a snapshot of an existing filesystem.

• Delete a snapshot.

• Access a snapshot under a dedicated directory name.

• Restore a filesystem from a snapshot.

• Create a snapshot of a snapshot (relevant for writable snapshots or read-only snapshots before being made writable).

• List the snapshots and obtain their metadata.

• Schedule automatic snapshots. For details, see Snapshot policies.

To access the hidden .snapshot directory, see Access the .snapshots directory.

Working with snapshots considerations

• Do not move a file within a snapshot directory or between snapshots: Moving a file within a snapshot directory or between snapshots is implemented as a copy operation by the kernel, similar to moving between different filesystems. However, such operations for directories will fail.

• Working with symlinks (symbolic links): When accessing symlinks through the .snapshots directory, symlinks with absolute paths can lead to the current filesystem. Depending on your needs, consider either not following symlinks or using relative paths.

• Snapshot estimated reclaimable space: The estimated reclaimable space represents the upper limit of capacity that can be freed by deleting a snapshot. It corresponds to the total size of data that is accessible from a snapshot but not from newer snapshots or the active filesystem.

  In snapshot chains without writable snapshots, deleting multiple consecutive snapshots (only the oldest N snapshots) releases the combined total of their respective Estimated Reclaimable Space values.

  Snapshots created before an upgrade to version 4.4 or downloaded from OBS may not have an Estimated Reclaimable Space value available.

Maximum supported snapshots

The maximum number of snapshots in a system depends on whether they are read-only or writeable.

• If all snapshots are read-only, the maximum is 24K (24,576).

• If all snapshots are writable, the maximum is 14K (14,336).

A system can have a mix of read-only and writable snapshots, given that a writable snapshot consumes about twice the internal resources of a read-only snapshot.

Some examples of mixing maximum read-only and writable snapshots that a system can have:

• 20K read-only and 4K writable snapshots.

• 12K read-only and 8K writable snapshots.

A live filesystem is counted as part of the maximum writable snapshots.

Related topics

Manage snapshots using the GUI

Manage snapshots using the CLI