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NDMP backups and dumps versioning - Details of expiration

Technote (FAQ)


Question

How is Tivoli Storage Manager applying versioning to NAS backups?

Answer

To backup NAS filer using NDMP protocol a Tivoli Storage Manager client NAS node needs to be defined to the Tivoli Storage Manager server. This Tivoli Storage Manager client node belongs to a policy domain as all other nodes.
Therefore Tivoli Storage Manager policies (like versioning) apply to Tivoli Storage Manager NAS backups, too.

Tivoli Storage Manager versioning applies to the complete NDMP dump only because the Tivoli Storage Manager server is not aware of the single objects included in the NDMP dump (except when reading the TOC).
To apply Tivoli Storage Manager versioning to single objects the single objects within the NDMP dump would need to have their own Tivoli Storage Manager server internal object ID assigned which is NOT the case.
In addition, if Tivoli Storage Manager versioning would apply to single objects within the NDMP dump something similar to aggregate compression had to be available to "delete" the invalid objects out of the NDMP dump which is NOT the case, too.

For a NAS filesystem, full and differential backups are grouped, with the full backup being the peer group leader.

If for example VEREXISTS = 4 and you do a full backup followed by 3 differentials then your Tivoli Storage Manager server database will have 4 versions of this backup image.
The next differential backup of the NAS filer will expire the full backup (but the Tivoli Storage Manager server is still keeping it internally, since it is needed to restore any of the differential images ).

The Tivoli Storage Manager server may store a full backup in excess of the number of versions you specified. When this happens, the full backup will stay in Tivoli Storage Manager database until all dependent backups have expired.

'QUERY NASBACKUP' will not show this extra version.

Use the undocumented 'SHOW VERSION' Tivoli Storage Manager server command to see this extra version.

Use the following command to examine the dependency of full image and differential image backups:

'show version nodename filespace_name'

/vol/vol1 : /NAS/ IMAGE (MC: default)
Inactive, Inserted 05/25/05 11:14:57, Deactivated 1900-01-01 00:00:00.000000
ObjId: 0.138114, GroupMap 00050000, objType 0x0b
Attr Group Leader, GroupId: 0.138114
Delta Group Leader, GroupId: 0.138114

We see this version is deactivated already (Deactivated 1900-01-01 00:00:00.000000), it should have expired, but it stays in the Tivoli Storage Manager server database because it is a delta group leader (GroupId: 0.138114) and the following delta member (GroupId: 0.138114) has not yet expired:

/vol/vol1 : /NAS/ IMAGE (MC: Default)
Inactive, Inserted 07/20/05 20:41:28, Deactivated 07/27/05 22:15:21
ObjId: 0.179387, GroupMap 00040001, objType 0x0c
Delta Group Member, GroupId: 0.138114
Attr Group Leader, GroupId: 0.179387

In the example above, Delta Group Leader represents the full image backup and the Delta Group Member the differential image backup.

Important to understand:
Although the already expired full and differential NAS backups can be seen, it is not possible to do a point in time (PIT) restore from the date of an expired full or differential backup! It is only possible to do a PIT restore from full and differential NAS backups that have not yet expired.

Document information

More support for: Tivoli Storage Manager
Server

Software version: All Supported Versions

Operating system(s): Platform Independent

Reference #: 1200154

Modified date: 28 March 2011


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