--On Saturday, February 08, 2003 16:12:45 -0500 "John R. Jackson" <jrj AT
purdue DOT edu> wrote:
>>> ADIC Scalar 100 - 4x Quantum DLT7000 Drives
>>> - the picker has a barcode scanner
>>> 120 DLT IV's
>>> ...
>
>>> dumpcycle 4 weeks # the number of days in the normal dump cycle
>>
>> Are you sure you want this? It means that each disklist entry (DLE) will
>> only
>> be gauranteed a full backup every 4 weeks. IT also means that if you need to
>> restore it you have to use up to 20 tapes to do it (since your running 5
>> days/
>> week)
>
> We run configs here with a four week cycle due to the quantity of data
> backed up per night. Simple math of bytes dumped divided by drive
> bytes/second. Something had to give, so it was the dumpcycle which
> has the effect of lowering the daily dump amount (and thus the time to
> dump it).
>
> DLT7000 drives are ~5 MBytes/s, so in a typical 8 hour backup window you
> can do at most ~140 GBytes (~4 tapes at 35 GBytes/tape). Those estimates
> are high, however, due overhead in various places.
If you have the luxury of enough holdingdisk space (as large as your
total backup, for example), then the tape speed becomes less relevant
since your backup window can end once it all goes to the holdingdisk,
and you can take the rest of the day to finish streaming it to tape.
>
> Geoff may have to use a larger dumpcycle than "normal". However, I
> agree with Frank that it should probably start smaller and only crank
> up if necessary.
>
> Also, the maximum number of tapes you will ever have to use for a restore
> is 10. Amanda never runs an incremental level higher than 9, so a full
> dump plus 9 incrementals is the worst case.
>
> Not that 10 is much more pleasant than 20 :-).
True, I didn't think about there only being 10 levels. But on an active
filesystem, won't you get to level 9 early in a long dumpcycle, increasing
the total size of your dumps? I can see that on some partitions you may
never even need an incremental, even on a long dumpcycle, but depending on
your mix of stable and churning filesystems, there has to be a maximum
length of dumpcycle before the total size actually starts increasing instead
of decreasing as the cycle is lengthened. Or is Amanda smart enough to
decide to schedule an early level 0 (or drop back to 8 or 7 or ..) instead
of yet another large level 9?
>
>>> use 290 Mb # how much space can we use on it
>>
>> If your DLEs are larger than this number then it won't do you any good ...
>
> I agree that 290 MBytes seems very small. The more you can give Amanda,
> the better it can parallelize/buffer the backup process.
>
> On the other hand, if this is all you have, it's better than nothing.
Yes, it would help on incrementals that would fit on it, I was just thinking
about the initial runs having to go directly to tape.
Frank
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