On 2006-06-30 09:24, Cyrille Bollu wrote:
> The backups will go directly to tape (i.e., slowly) if the _entire_
backup
> image doesn't fit on the holdingdisk.
Sorry for asking but, why do you say backuping directly to tape is slow?
I guess he's doing local backups (ie: The 700GB are not sent over the
network every full backups).
In this configuration what would be the benefit of having an holding disk?
Reading from holdingdisk files (a few large files, proabably even from
a separate filesystem that is not fragmented) is much quicker than
what a real backup is doing: stat()-ing files scattered all around,
reading small files, putting it all together, and piping through gzip
(or bzip2 for the brave people).
The tapedrive (LTO2) can handle a sustained 20 MByte/sec throughput
(at least that is what amtapetype measured).
Most affordable hardware cannot reach that speed with the above pipe.
I'm currently trying to backup about the same amount of data with a Dell
LTO-3 and cannot go faster than 20MB/s (see the thread "tar's default
block size & shoe-shinning").
Is that without a holdingdisk at all?
If with holdingdisk, do you read and write to holdingdisk at the
same time? (I mean, can the holdingdisk subsystem handle both
reading one file at LTO3-speed of 80 Mbyte/sec and to writing
several other holdingdiskfiles?)
One of the possibilities to try is to augment the number of RAM
tapebuffers that taper uses in amanda.conf:
tapebufs 20 # default: 20 buffers of 32 Kbytes each.
Find out how much RAM can spend on this part (it is implemented as
a shared memory region), and make that really really large: instead
of 20*32Kbyte (=640 Kbytes), make it 128 Mbyte, or 4096 tapebufs
or something alike. That should result in needing only once every
second or so to read from disk.
--
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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