JGillTech wrote:
> Preston,
>
> Thanks for the clarification. To make sure I understand, let me apply to a
> hypothetical situation:
>
> I have a 2 week retention period. Full backups are conducted on Sunday, with
> incremental throughout the week. If I ran a full backup on week 1, the
> expiration would be two weeks from that date. However, because of the
> dependency chain the actual expiration will be 3 weeks (the date of the last
> incremental in the chain).
In this situation, you will have backups UP TO 3 weeks old in your system.
At the end of Sunday, you have just completed your successful full
backup, so the backup you took 3 weeks ago has now expired. You can
restore any backup within the last two weeks and the oldest backup still
retained is two weeks and a few hours old.
On Saturday, NetWorker still promises you that you can restore your
system to the way it was two weeks ago. This is what we call a
point-in-time recovery. However if you wanted to do this recovery you
would need the full backup that you took 20 days ago as well as the
incrementals from 19, 18, 17, 16, and 15 days ago, in order to restore
your system to the way it was 14 days ago.
Varying this a little, if you had chosen to run differential (or a
numbered level backup in NetWorker terms) backups rather than
incrementals, you would need less of those tapes to run your
point-in-time backup. You would still need that full from 20 days ago,
but only the differential from 15 days ago. Hence the differentials from
19, 18, 17, and 16 days ago would have expired, but the full would still
be valid. NetWorker knows it can expires these backups and just keep the
ones necessary for the point-in-time recovery.
If a full backup fails and you don't re-run it, you will need to add a
further week on to the age of the oldest full so that NetWorker can
still provide you this point-in-time recovery. In this case you may need
rather a lot of your incrementals and the recovery could take quite some
time.
The mechanics of expiring a save set are also relevant. NetWorker does a
daily tidy-up, using the nsrim command. You may have save sets that are
ready to expire because of dates and dependencies, but this will not
actually take place until nsrim next runs. You can of course run nsrim
manually if your want to expedite this.
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