[ILUG] Dump very slow across gigabit network

[David Wilson]

What kernels are the machines running? Recent 2.6 kernels had improved
sliding window algorithms merged for high speed/high latency links
(Google about it, I know little off the top of my head). Try tweaking
/proc/sys/net/ipv4 tunables regarding window size (I believe the
defaults are fairly useless on high speed links).

Also consider playing with ssh, for instance, blowfish encryption can
be faster on certain processors compared to the default (I forget what
the default is).

Can you reach close to wire speed using something like netcat -u? How
congested is the network otherwise? How cheap were your switches?
etc...

If you dump locally, how long does the dump take to complete (i.e.
have you ruled out the possibility the machine itself has a
software/driver proplem?)


David.

On 14/09/2007, Conor Daly <conor.daly_ilug at cod.homelinux.org> wrote:
> I'm using dump to backup a number of filesystems to a tape hosted on a
> remote machine.  The machine being backed up is still in commissioning so
> it hasn't got its full complement of data yet.  Last night, one 300Gb
> filesystem had about 21Gb used.  It took 3.5 hours to dump at an average
> rate of 1530 kB/s (according to dump).  By my calculations, if this
> filesystem fill completely, it will take 57 hours to backup.
>
> The dump runs like this:
>
> Remote machine mounts the tape
> local machine does:
>
> export RSH=ssh
>
> dump -0 -f remote:/dev/nst0 /filesystem
>
> local and remote machines are connected by a crossover cable.  Their
> connections show up in dmesg output as running at 1000bit full duplex.  I
> can do:
>
> scp /path/to/7.1Gb_file remote:
>
> and get about 40Mb/s throughput which translates to about 2 hours for
> 300Gb.
>
> Any clue why dump is taking so long?  The filesystem it's dumping has not
> too many files, each file is fairly large (~2Gb).
>
> Running dump on RHEL 5
>
> Conor
>
>
> --
> Conor Daly <conor.daly at cod.homelinux.org>
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