Jon LaBadie wrote:
Kind of a "best practice" or "common usage" query.
For those of you using vtapes, how have you chosen
to specify the size of a single vtape?
A while ago, perhaps 1-2 yrs when vtapes were starting
to be used more regularly, the comments seemed to be
"divide the available space by the number of vtapes".
This ensured that the file system would never run out
of space but meant that some available space is "wasted".
In contrast, when I 'played' with vtapes a year or more
earlier, I just specified a huge size, knowing it would
"never" be exceeded. However a possibility was that I
would run the file system out of space if many vtapes
were pretty full.
Gene H., as I under stand it, uses a third variation.
He wants X number of vtapes and wants them pretty full.
To achieve this he adjusts the dumpcycle & runspercycle
parameters.
How are current users sizing their vtapes and what has
been their experience in disk usage?
Sometimes there are other constraints on the size of a vtape.
E.g. you want them to fit on a DVD, or make a copy of them to
a real tape using dd. In that case I use those constraints: the
size of a DVD or of the physical tapes).
Otherwise, I specify a quite large value, so that even on a
day when Amanda needs to schedule a huge DLE, there is still enough
space to fit on one single vtape.
In the long run, it is the average value of a vtape that is important.
Note that when you write a dump to a vtape, and you hit EOT, the
last incomplete part of a dump is not erased, just like a real tape.
So, many "incomplete" parts on a too small vtapes do take up real
diskspace (and time too!). That's why I try avoid that situation.
On a vtape this is easy.
Maybe that could be fixed by a little shell script that erases those
last useless incomplete parts to free diskspace... Hmmm TODO...
(: can you tell I'm thinking about using vtapes :)
USB-1 can handle about 1 Mbyte/sec, which is already twice as fast
as a DDS2-tape; USB-2 is about 6-8 Mbyte/sec in my test env.
--
Paul Bijnens, xplanation Technology Services Tel +32 16 397.511
Technologielaan 21 bus 2, B-3001 Leuven, BELGIUM Fax +32 16 397.512
http://www.xplanation.com/ email: Paul.Bijnens AT xplanation DOT com
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