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Re: [Amanda-users] Advice needed on Linux backup strategy to LTO-4 tape
2009-08-14 15:37:38
Cyrille Bollu wrote:
Here's my (very) small personnal experience:
A few years ago, when I tried it, I couldn't enable server-side
software compression while bypassing the holding disk with my IBM
ULTIUM LTO-3 drive: Tape speed was sinking to about 5MB/s.
My backup server was a Dell PowerEdge 2850 with 4 Intel Xeon 3GHz and
8MB RAM using RHEL-4.0 and amanda-2.4.4p3-1.
Maybe did I do something wrong at that time (I just had 1 try). Beware
though.
That actually makes perfect sense.
By not using a holding disk, you are disabling Amanda's ability to run
multiple things in parallel. The tape device now controls everything.
That is to say, you cannot do a backup without streaming it to the tape.
So, you cannot do more than one at a time. Furthermore, as that one
backup gets done, the compression has to be done as it is being streamed
to the tape. So all the processes from reading a remote disk, to
transferring it over the network, to compressing it, to writing it to
the tape are all tied together in a single pipe. Any slowdown along that
pipe will affect everything else. When the tape doesn't get what it
needs to keep going, it will stop and then have to start up again and
reposition, and then you get shoe shining.
When you use a holding disk, Amanda can stream multiple backups to the
holding disk simultaneously. It can compress them there when it has them
and do it in parallel with other processes. Once it has something ready
to go to tape, it can dd it straight from the disk to the tape as an
independent process in parallel with the other things that are going on.
That final step out to the tape is no longer constrained by any of the
other steps along the way. Now all you have to worry about is tuning
various pieces of hardware and software to get the throughput you want.
--
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Chris Hoogendyk
-
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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