Control whether new tapes are used or old one are overwritten on next full backup
Posted by Sven Koester on 13 May 2009 9:00
We are often asked how PresSTORE controls whether new tapes are used in the next full backup or whether old tapes are overwritten and reused.
Here is a brief description:

This depends on two settings and on the state of the volumes.
Those settings are
  • the recycling policy of the pool -and-
  • whether new volumes should be used for a full backup or whether the backup should append to the existing volumes.
The volume states are
  • whether blank tapes are available -and/or-
  • whether there are tapes that are recyclable.

In case data is to be appended to the tapes and there is still free space on at least one of the tapes of the pool, these tapes will be used to write the data - oldest first.
If, on the other hand, "Use new media" is set in the backup plan, the full backup will look for an empty tape to use.

Independently from the above, if the recycling policy is set to "When volumes are needed" in the media pool, PresSTORE attempts to keep the data on tapes as long as possible. This means, that if there are blank volumes, the preference is to use those before reaching to recycle a volume to make new space available. If, on the other hand, "When expiration date is reached" is set, all the volumes of the required pool that can be recycled, will be recycled before the job starts to look for tapes to write on.

This all is true, provided the tapes are available in the Jukebox for any of the above operations. So making tapes available or unavailable by exchanging the tapes in the Jukebox has the highest priority.
If the tapes that have been written the whole week are removed from the jukebox and replaced with empty ones, or recyclable ones of the same pool before the full backup runs, the backup will use the replaced tapes according to the policies described above.

That is why one pool usually suffices and one can achieve a two (or many) tape set policy by simply exchanging the tapes in the changer.

One word of advice: PresSTORE will automatically re-inventory the state of the changer after a manual intervention, e.g. replacing the tapes.It is, however, advisable to run an manual inventory job once you have exchanged the tapes to ensure a more optimal operation.

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