Hp LeftHand P4000 Virtual SAN Appliance Software User Manual download pdf (Page 41)

NOTE: Retention of snapshots affects the amount of space that is used in the cluster of storage

systems. Balance the number of snapshots to retain with the amount of space you are willing

to use. You can still access remote snapshots or tape backups if you want to roll back to a

snapshot that you did not retain.

• Retain remote snapshots in the backup location to facilitate fast recovery of backed-up data.

If you retain a number of remote snapshots after a tape backup is created, you can access

the data without going to the backup tape.

Example configuration

• Retain three primary snapshots. This enables you to roll the primary volume back, yet it requires

a relatively small amount of space on the primary cluster.

• Retain up to a week's worth of remote snapshots on the backup cluster.

• For snapshots older than one week, go to the backup tape.

Achieving nondestructive rollback

As discussed in “Rolling back primary and remote volumes” (page 29), rolling a snapshot back

to a volume requires you to delete any snapshots that were created since the snapshot that you

roll back to. For example, suppose you created snapshots of a volume on Monday, Tuesday, and

Wednesday. On Thursday, if you roll the volume back to Monday's snapshot, then the snapshots

from Tuesday and Wednesday must be deleted first.

You can use Remote Copy to roll a volume back to an old snapshot without losing the interim

snapshots. Because Remote Copy creates two sets of snapshots—primary and remote snapshots—you

can roll a volume back to a snapshot and still retain the other set of snapshots.

Configuration for nondestructive rollback

To use remote snapshots for nondestructive rollback:

• Create a remote snapshot schedule.

• In the schedule, specify the same retention policy for the primary and remote snapshots. This

ensures that you have copies of the same number of snapshots in your primary and remote

locations. Any snapshots destroyed during rollback of one volume remain intact on the other

volume. See an illustration of a nondestructive rollback configuration in “nondestructive rollback

example” (page 42).

Using Remote Copy for off-site backup and recovery 41

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Hp LeftHand P4000 Virtual SAN Appliance Software User Manual Page 41