On Tue, Jul 25, 2006 at 07:29:02AM +0200, Sebastian Kösters wrote:
> Hi!
> 
> A short question.
> 
> I would like to have the possibility to recover a backup thats 14 Days old.
> 
> I want to use virtuel tapes and a tape-changer for this.
> 
> Every 7 Days Amanda should do a full-backup.
> 
> Am i right that i need a tapecycle of 14 a runspercycle of 13 and a
> dumpcycle of 7?
> 
> If not, what must i set at tapecycle, runspercycle and dumpcycle to get this
> work?

Only one is certain, dumpcycle 7, gives you a level 0 (full) backup
of each DLE ``at least'' once every 7 days.

runspercycle is how many times you will have crontab run amdump
during each dumpcycle.  If you do it once every day, runspercycle
should be 7.  If only on weekdays, 5, if only Mon, Wed, Fri, 3.

Your setting of runspercycle 13 would be most unusual.
With dumpcycle 7, it would suggest twice a day except only once
on ?tuesdays?

Lets assume daily runs, even on weekends, so runspercycle 7.
With dumpcycle 7 that matches my two settings.

We still can't determine a minimum value for tapecycle without one
other parameter, runtapes.  This is how many tapes, physical or
virtual, amanda might use for each run of amdump.  Not how many
it will use, how many it is allowed to use if needed.  My nightly
backups generally fit a single tape.  But occassionally it overflows
to a second.  So I have runtapes 2.

Now the calculation for tapes needed in the cycle is essentially:

  # cycles to retain X runspercycle X runtapes

I wanted 4 or 5 cycles worth of backups (about a month).  That would
be 5 X 7 X 2 == 70.  But, because I determined that I would not be
using a second tape except occassionally, I'm comfortable with a
little more than 1/2 that number, I have a tapecycle of 40.

If my environment adds a lot more data, or some more clients, either
I will not be able to retain 5 cycles worth of backups, or I will
have to add another external disk for more vtapes.

HTH

-- 
Jon H. LaBadie                  jon AT jgcomp DOT com
 JG Computing
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