When creating and using
snapshots, review the following requirements and guidelines.
Snapshot images and snapshot groups
Snapshot consistency group
- A snapshot consistency group contains one snapshot group for each volume that is a member of the snapshot consistency group.
- You can associate a snapshot consistency group with only one schedule.
- If you delete a snapshot consistency group that has a snapshot schedule, the snapshot schedule is also deleted.
- You cannot individually manage a snapshot group that is associated with a snapshot consistency group. Instead, you must perform the manage operations (create snapshot image, delete snapshot image or snapshot group, and rollback snapshot image) at the snapshot consistency group level.
Base volume
- A snapshot volume must have the same Data Assurance (DA) and security settings as the associated base volume.
- You cannot create a snapshot volume of a failed base volume.
- If the base volume resides on a volume group, the member volumes for any associated snapshot consistency group can reside on either a pool or volume group.
- If a base volume resides on a pool, all member volumes for any associated snapshot consistency group must reside on the same pool as the base volume.
Reserved capacity
- Reserved capacity is associated with only one base volume.
- Using a schedule can result in a large number of snapshot images. Make sure you have sufficient reserved capacity for scheduled snapshots.
- The reserved capacity volume for a snapshot consistency group must have the same Data Assurance (DA) and security settings as its associated base volume for the snapshot consistency group member volume.
Pending snapshot images
Snapshot image creation might remain in a Pending state in the following conditions:
- The base volume that contains this snapshot image is a member of an asynchronous mirror group.
- The base volume is currently in a synchronization operation. The snapshot image creation completes as soon as the synchronization operation is complete.
Maximum number of snapshot images
- If a volume is a member of a snapshot consistency group, System Manager creates a snapshot group for that member volume. This snapshot group counts towards the maximum allowable number of snapshot groups per base volume.
- If you attempt to create a snapshot image on a snapshot group or snapshot consistency group, but the associated group has reached its maximum number of snapshot images, you have two options:
- Enable automatic deletion for the snapshot group or snapshot consistency group.
- Manually delete one or more snapshot images from the snapshot group or snapshot consistency group and retry the operation.
Auto-deletion
If the snapshot group or snapshot consistency group is enabled for automatic deletion, System Manager deletes the oldest snapshot image when the system creates a new one for the group.
Rollback operation
- You cannot perform the following actions when a rollback operation is in progress:
- Delete the snapshot image that is being used for the rollback.
- Create a new snapshot image for a base volume that is participating in a rollback operation.
- Change the associated snapshot group’s Repository-Full Policy.
- You cannot start a rollback operation when any of these operations are in progress:
- Capacity expansion (adding capacity to a pool or volume group)
- Volume expansion (increasing the capacity of a volume)
- RAID level change for a volume group
- Segment size change for a volume
- You cannot start a rollback operation if the base volume is participating in a volume copy.
- You cannot start a rollback operation if the base volume is a secondary volume in a remote mirror.
- A rollback operation fails if any of the used capacity in the associated snapshot repository volume has unreadable sectors.