Snapshots Overview

The initial snapshot for a volume uses no space because it shares its original data with the volume from which it was taken. Each successive snapshot consumes some amount of space because it captures the changes that occurred on the volume. The changed blocks are compressed to reduce capacity consumption.

Consider the change rate of the applications using the volume, the assigned replication strategy, and the snapshot retention to determine the amount of space you need for snapshots. You can retain numerous snapshots in most environments.

A snapshot reserve represents the amount of space that you allocate (pre-reserve) from the general pool for snapshots of a volume. Each successive snapshot captures and stores changes to the volume contents. Snapshot reserve space can be increased if needed. When the snapshots exceed the amount of space reserved, space is then used from the general storage pool.

The optional snapshot quotas determine how much of the volume can be consumed by snapshots. For example, you may want to allow no more than 10% of the volume space to be used for backup. Setting the snapshot quota to 10% ensures this volume is not exceeded. The actual amount of space you need depends on the application using the volume and the volume collection to which it is assigned.

If a volume is approaching the quota limit, an event is logged. When enforcement is enabled, the volume administrator can determine what follow-up actions to take, such as preventing users from accessing more disk space or allocating additional disk space.

Initiators access online snapshots just like they access online volumes. To access snapshot data, set the snapshot online and log the initiator into the snapshot.

When you delete a volume, the snapshots that are associated with that volume are also deleted. If the volume has online snapshots, they must be taken offline before you can delete them.