[Techtalk] Dump very slow over Gigabit connection

Conor Daly conor.daly-linuxchix at cod.homelinux.org
Fri Sep 14 13:53:29 UTC 2007

On Fri, Sep 14, 2007 at 01:45:29PM +0200 or so it is rumoured hereabouts, 
Wim De Smet thought:
> On 9/14/07, Conor Daly <conor.daly-linuxchix 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.
> >
> Can you check what the compression settings are at? Also, have you
> tried doing a local dump? If you start dump, have a look at iostat and
> top output to see where it might be spending its time. Personally I
> dump with bzip and it really slows things down as it makes the process
> partly cpu bound.

No compression.  Tried local dump and various permutations.  It goes
something like this:

Method:				   speed (MB/s)	ratio
scp local file to remote disk:	   40		1
dump to local disk:		    7.5		0.19
dump to remote disk:		    1.5		0.04
dump to remote tape:		    1.5		0.04
dump remote disk to remote disk:   33.5		0.84
dump remote disk to remote tape:   16		0.4
cp local file local disk:	   49		1.22
cp remote file to remote disk:	   14.3		0.36
cpio to local disk:		   43		1.08
cpio to remote disk:		    0.03	0.0009
tar and dd to remote disk:	   17		0.43
cat tarball and dd to remote disk: 34		0.85
tar and dd to remote tape:	    7		0.18
cat tarball and dd to remote tape:  8.5		0.21

local is the client machine that I want to backup.  Remote is the machine
that hosts the tape drive.  anything listed as remote to remote happens
entirely on the remote machine with no network involvement.  Anything
listed as local to local happens on the local machine with no network
involvement.  local to remote goes across a gigabit network via crossover
cable (no switches or other hosts involved).


Conor Daly <conor.daly at cod.homelinux.org>
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