Technical data

Using BACKUP
11.15 Backing Up User Disks
Volume shadowing checks for geometries and maximum logical block numbers
(LBNs) on devices. This enables devices such as the RZ28 and the RZ28B to
operate in the same shadow set. Even though their device IDs differ, their
geometries and maximum LBNs will match when configured on like controllers
(two HSJ controllers, for example).
When you create a shadow set, individual users access it as a virtual unit. For
example, you could create a virtual unit DSA1 that consists of the disks named
DUA1:, DUA2:, and DUA3. Users cannot access the individual shadow set
members directly, but can perform operations on the virtual unit (DSA1:).
Because of the way volume shadowing duplicates data on each disk in the shadow
set, there are special considerations for backing up a shadow set. One strategy
for backing up shadow sets involves using the OpenVMS Backup utility.
Caution
Do not attempt to back up a shadow set by dismounting an individual
shadow set member or by backing up an active shadow set member. You
must dismount the entire shadow set and re-create it less one shadow set
member. If you do not follow this restriction, the resultant backup copy
may contain inconsistent data.
How to Perform This Task
The proper procedure for using BACKUP to back up a shadow set is described in
detail in the Volume Shadowing for OpenVMS manual, and can be summarized
as follows.
Note
You cannot perform an incremental backup using this procedure because
the backup record date is overwritten when you add the disk volume back
into the existing shadow set.
1. Make sure that all shadow set members are full members; none of the
members should be in a merge or copy state.
2. Dismount the entire shadow set.
3. Re-create the shadow set less one member. The data on the excluded member
will mirror the data on the shadow set members.
4. Mount the former shadow set member for the backup.
5. Perform an image backup on the former shadow set member.
6. Dismount the former shadow set member when the backup is complete.
7. Add the shadow set member that you backed up.
11–44 Using BACKUP