## About Volume Snapshots

A volume snapshot is a copy of the data on a volume at the moment you create the snapshot. The implementation of a snapshot on this system is a copy-on-write or dependent copy. In this type of snapshot, write operations to the primary volume causes the system to copy the data to the snapshot reserve space also. When a write operation occurs to a data block on the primary volume in which the data has not changed since the snapshot was created, the system does the following:

- Copies the data about to be changed to the snapshot reserve space
- Writes the new data to the primary volume
- Adds a record to the snapshot bitmap indicating the new location of the old data

When a host sends a read request to the volume snapshot, the system checks whether the requested blocks have changed on the primary volume since the point in time when the snapshot was created. If they have changed, the read request is satisfied from the data stored in the snapshot reserve space. If the data has not changed, the read request is satisfied from the primary volume. Volume snapshots can also accept write operations. Write operations to a snapshot volume are stored in the snapshot reserve space.

You can work with these volume snapshots as you would any other volume, with the exception that you cannot take a snapshot of a snapshot. Each snapshot can be accessed independently by other applications. A snapshot can be mounted on another server and used in the following ways:

- Backing up snapshots of data to reduce downtime for backup operations

Backing up snapshots, rather than online data, enables critical transactions to keep running during the backup process. Mount the snapshot to the backup server, and then back up the snapshot's data to tape.

- Performing data analysis and testing applications with actual, current data.

Instead of working with operating data or interfering with critical transactions, use the most recent snapshot for analysis or testing of data.

- Restarting applications from the snapshot volume

If an application problem causes bad data to be written to the primary volume, restart the application with the last known good snapshot volume until it is convenient to perform a full recovery.

Note -

A snapshot of data is not suitable for failure recovery. Continue to use offline backup methods to create full-volume backup copies.

To see the current snapshots for a volume, go to the Snapshot Summary page, as described in Displaying Volume Snapshot Information.

### Related Topics

- Managing Volume Snapshots
- Planning a Volume Snapshot