[ILUG] Dump very slow across gigabit network

[Pádraig Brady]

Conor Daly 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


I never used dump before, and had a quick look at the man page.
Laugh! I would rather look at a network trace to see
the packets traversing the network and the latencies involved.
Why are you using tapes anyway. Aren't (removable) hard disks
much more compatible/performant/cheaper/sane these days?

Some links you may find useful:

http://dump.sourceforge.net/isdumpdeprecated.html
http://www.pixelbeat.org/speeds.html
http://www.linux.ie/old-list/31339.html
https://bugzilla.mindrot.org/show_bug.cgi?id=1337