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Re: [Amanda-users] Advice needed on Linux backup strategy to LTO-4 tape
2009-08-17 09:14:46
Rory Campbell-Lange wrote:
On 14/08/09, Frank Smith (fsmith AT hoovers DOT com) wrote:
Chris Hoogendyk wrote:
Amanda will do the compression for you. You define it in the dumptype in
amanda.conf. If you have a holding disk, then it will compress the data
as it goes onto the holding disk. If you don't have a holding disk, then
you might have issues with being able to stream a backup to tape,
compressing it on the fly. Even with a really fast cpu, I don't know if
you can maintain the throughput to drive LTO4 at a good speed.
You might want to consider configuring for client compression. Not
only will that give you more CPU for feeding your tape, it also
minimizes network bandwidth. As usual, YMMV, it all depends on where
the bottlenecks are in your environment.
In our case the server _is_ the only client, with up to 30TB of direct
attached storage, with the storage running at between 80MB/s and 120MB/s
access speeds (Bytes rather than bytes).
I don't know if this is fast enough to deal with a SAS connected LTO4
drive, particularly if it is doing software compression along the way.
With reference to Chris Hoogendyk's email "clarification on
parallelism", I am very curious to learn if Amanda "...still require[s]
a DLE to be completed to holding disk before it will send any of it to
tape..." In our case this is a particularly important question as,
although we can add in more AoE storage for a DLE, this will only run at
the speeds above. Do we need a 1TB SAS disk array too?
You will get the best performance if you can do that. If the disk that
is being copied to tape can give the speed the tape needs, that's going
to do a better job of keeping things moving.
You have a couple of options.
You can go without a holding disk, and then each DLE will be streamed
sequentially to tape. This will stretch out your backups. It will also
mean that any compression you do in software will be done in line with
that sequential stream. Your system may not be able to keep that all
flying fast enough for the tape, and you may end up with shoe shining
and very low speeds. You can certainly try it and see what happens. If
(when?) that fails, you could try using hardware compression on the tape
drive. The backups will still be sequential, one DLE streaming to tape
at a time, and if your drives can't keep up, it will be slower than you
might like. But, at least you are not dealing with network backups.
The option I would try, budget allowing, would be to add a couple of SAS
drives to be used as holding disks. Then break up your DLEs so that each
DLE is substantially smaller than the holding disks. Then Amanda can run
them in parallel, compress them on the holding disk, and then stream
completed, compressed DLEs from the holding disk to the tape.
I wouldn't put the holding disks in raid.
--
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Chris Hoogendyk
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O__ ---- Systems Administrator
c/ /'_ --- Biology & Geology Departments
(*) \(*) -- 140 Morrill Science Center
~~~~~~~~~~ - University of Massachusetts, Amherst
<hoogendyk AT bio.umass DOT edu>
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Erdös 4
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