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PowerStore features pointer-based immutable snapshots, meaning that the data is read-only and can never be modified. These snapshots can be used for restoring individual files or the entire file system back to a previous point in time. Because these snapshots leverage redirect-on-write on technology, no additional capacity is consumed when the snapshot is first created. Capacity only starts to be consumed as data is written to the file system and changes are tracked.
Snapshots can be taken manually or by the integrated scheduler. Manual snapshots can be created at any time on the file system properties page. Scheduled snapshots can be configured by creating a protection policy with one or more snapshot rules and applying the policy to the file system. Starting with PowerStoreOS 3.5, secure snapshots can be taken by a snapshot rule, but secure snapshots are not supported on file systems. If a protection policy containing a secure snapshot rule is applied to a file system, the policy runs and creates standard snapshots instead.
When a snapshot is created, it can be configured to have no automatic deletion or retention until a specific date and time. If retention is set, the snapshot is automatically deleted upon reaching the retention date. This retention setting does not prevent the snapshot from being deleted before the retention date.
All snapshots that are created by a protection policy must have a retention date. The maximum retention date varies depending on how often the snapshots are scheduled. Each file system supports up to 256 snapshots so the combination of the snapshot frequency and retention cannot be configured to exceed this number.
For file snapshots, there are two access types available:
Both protocol- and snapshot-type snapshots are read-only. To access the data on a protocol snapshot, a share must be created. Once the share is created, the snapshot can be mounted on the host and accessed as if it were a read-only file system.
Snapshot-type snapshots have integration with Windows and UNIX systems to enable self-service restores. On UNIX systems, users can access snapshot data by going to the .snapshot directory. On Windows systems, users can access snapshot data using the Previous Versions tab, as shown in Figure 40.
Both protocol and snapshot type snapshots can be used for individual file and folder restores by copying the data off the snapshot back to the file system. Also, both types of snapshots can be used to restore the entire file system back to that point in time. When restoring the entire file system, a backup snapshot of the current file system data is taken by default.
Snapshots can be refreshed at any time. Refreshing the snapshot overwrites the contents of the snapshot with the data that is currently on the file system. Refreshing a snapshot only updates the data contents of the snapshot so the snapshot properties do not change.
For more information about snapshots, see the Dell PowerStore: Snapshots and Thin Clones white paper.