JC Simonetti wrote:
Hi all! I'm stuck while reading my today Amanda report: 27 Gb backed
up today that did not fit in 40 Gb (2 tapes of 20 Gb)! Well... It's
normal, since: nearly all data were onto tape 1 (about 7 Gb). Another
DLE tried to go on this tape, but too large (14 Gb). So it took the
next tape and went on it. And the last DLE, that was around 7 Gb, did
not fit onto this tape, and failed (I configured Amanda to use 2
tapes).
In recent (I believe 2.4.3 or later) version there is taperalgo
and dumporder to tune this.
In my config I have set the options:
inparallel 10 # the number of dumpers
taperalgo largestfit
dumporder "TTTTTTTTTT" # as many T's as you have dumpers
And my the first 2 of my 3 tapes are filled near 100%!
I chose dumperorder T: longest first, because that way the slowest
computer is finished faster. If you have another mix of slow/fast
computers with small/large filesystems, then maybe "S" (largest first)
could improve the tape usage in some boundary cases.
The taperalgo setting only works good enough if you have many images
to choose from. Taperalgo chooses only from those images that have
finished dumping. For an easy explanation, lets asume you start 10
dumpers (inparallel 10) and choose to dump the largest first
(dumporder "SSSSSSSSSS") and all your filesystems on all your computers
have the same dumprate. The first one that will be finished is the
smallest of those 10. Taperalgo has only one image to choose from,
and starts taping this one. While it is taping this image the next
one to finish dumping is the next to smallest one, etc.
By the time taper finished its first image, it can choose between,
let's say 5 images. This is the time when you really see taperalgo
can optimize your tapeusage.
If you're in the case where all the smaller dumps finish too early,
then you can even decrease the number of dumpers.
The default dumporder is (I believe) "sssSSSSS": if you have 5 large
systems, and many smaller, it could happen that all the small dumps
are finished before the first large one arrives. Then you have all
your small dumps in the beginning of the tape, and the large dumps
at the end. If a large dump hits EOT, it has to start all over again
on the next tape; like you noticed, that could waste a lot of tape.
Because it's easier for amanda to fiddle with many smaller pieces
than a few large ones, I break up my very large filesystems in a few
smaller ones too.
--
Paul Bijnens, Xplanation 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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