Using snapshots

What snapshots are

Snapshots are a standard feature of Data ONTAP. A snapshot is a frozen, read-only image of the entire Data ONTAP file system (or WAFL® volume) that reflects the state of the file system at the time the snapshot was created.

Snapshots are the first line of defense for backing up and restoring data.

Caution
You must save contents of host file system buffers to disk before taking snapshots or using other data protection applications, such as dump, SnapMirror, SyncMirror, SnapVault, and so on, on the filer.

Reasons to take snapshots

Data ONTAP takes snapshots so that you can back up LUNs to tape or to a SAN host that is acting as a backup server.

If data corruption is found, a LUN or set of LUNs can be restored from a snapshot using the SnapRestore feature. Snapshots can also be replicated to remote sites, using the SnapMirror feature, in case they are needed for disaster recovery.

How snapshots are used in the SAN environment

Snapshots are always consistent with regard to the underlying WAFL file system. Prior to creating a snapshot, you must quiesce the application or file system using the LUN (which flushes the host filer system buffers to disk), so that the snapshot is consistent with regard to the application.

In Data ONTAP 6.3 and later, volumes can be space reserved, which means that if free space within the volume is below a certain threshold, snapshots cannot be taken.

Note
On Windows hosts, you can use SnapDrive 2.0 or later to save the contents of the host file system buffers to disk and create snapshots. See the SnapDrive Installation and Administration Guide.

How writable snapshots are used to copy LUNs for data protection

Only writable LUNs can be mapped to a host. Therefore, to map a LUN that exists in a snapshot, the snapshot must be made writable, that is, it must be made available in the active WAFL file system.

Network Appliance recommends that you do not use scheduled snapshots to replicate LUNs on a regular basis because multiple LUNs from different hosts can exist on the same WAFL volume.

To create, find, delete, or rename specific snapshots, see the detailed information about snapshots in the Data ONTAP 6.4 Data Protection Guide.