Incremental Restore


Only the latest image backup and the latest cumulative backup tape are used in the restore operation. The destination disk will be completely overwritten in this process. The image backup tape is restored to disk first. This is the same operation as shown previously. Then the latest cumulative backup tape is restored. That command is similar to the following:

    $ BACKUP/INCREMENTAL/VERIFY -    _$ MUA400:CUM.SAV/REWIND/LABEL=CUMULA -    _$ DUA0: 

If restoring differential save sets, as similar command is repeated for each tape, starting with the most recent.

To compare the various backup methods, consider both the backup and the restore operations. A differential backup is the smallest and therefore takes the least amount of time to perform. The cumulative backup is sort of a sum of differential backups. It is larger than a differential backup and takes longer to produce. The image backup is the largest and takes the most time to generate.

An image backup is the fastest to restore because only one save set is required. If cumulative backups are performed, first the image backup is restored and then the latest cumulative backup is restored. If differential backups are performed, first the image backup is restored and then the latest differential backup is restored, then the one previous to that, and so forth until all differential backups are restored. This latter option obviously takes the most amount of time. Thus, the system manager must trade off backup time and restore time when deciding a backup strategy.




Getting Started with OpenVMS System Management
Getting Started with OpenVMS System Management (HP Technologies)
ISBN: 1555582818
EAN: 2147483647
Year: 2004
Pages: 130
Authors: David Miller

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