Administering volume snapshots 315

Cascaded snapshots

Figure 9-6

Using a snapshot of a snapshot to restore a database

1.Create instant snapshot S1 of volume V vxsnap make source=V

Original

 

Snapshot

volume

 

volume of V:

V

 

S1

2. Create instant snapshot S2 of S1

vxsnap make source=S1

Original

 

Snapshot

 

Snapshot

volume

 

volume of V:

 

volume of S1:

V

 

S1

 

S2

3. After contents of V have gone bad, apply the database redo logs to S2

Apply redo logs

Original

 

Snapshot

 

Snapshot

volume

 

volume of V:

 

volume of S1:

V

 

S1

 

S2

4.Restore contents of V instantly from snapshot S2 and keep S1 as a stable copy vxsnap restore V source=S2

Original

 

Snapshot

 

Snapshot

volume

 

volume of V:

 

volume of S1:

V

 

S1

 

S2

If you have configured snapshots in this way, you may wish to make one or more of the snapshots into independent volumes. There are two vxsnap commands that you can use to do this:

■vxsnap dis dissociates a snapshot volume and turns it into an independent volume. The volume to be dissociated must have been fully synchronized from its parent. If a snapshot volume has a child snapshot volume, the child must also have been fully synchronized. If the command succeeds, the child snapshot becomes a snapshot of the original volume. Figure 9-7illustrates the effect of applying this command to snapshots with and without dependent snapshots.