PowerScale OneFS Web Administration Guide

Reducing snapshot disk-space usage

If multiple snapshots contain the same directories, deleting one of the snapshots might not free the entire amount of space that the system reports as the size of the snapshot. The size of a snapshot is the maximum amount of data that might be freed if the snapshot is deleted.

Deleting a snapshot frees only the space that is taken up exclusively by that snapshot. If two snapshots reference the same stored data, that data is not freed until both snapshots are deleted. Remember that snapshots store data contained in all subdirectories of the root directory; if snapshot_one contains /ifs/data/, and snapshot_two contains /ifs/data/dir, the two snapshots most likely share data.

If you delete a directory, and then re-create it, a snapshot containing the directory stores the entire re-created directory, even if the files in that directory are never modified.

Deleting multiple snapshots that contain the same directories is more likely to free data than deleting multiple snapshots that contain different directories.

If multiple snapshots contain the same directories, deleting older snapshots is more likely to free disk-space than deleting newer snapshots.

Snapshots that are assigned expiration dates are automatically marked for deletion by the snapshot daemon. If the daemon is disabled, snapshots will not be automatically deleted by the system. It is recommended that you do not disable the snapshot daemon.