dump performance - 4.6-RELEASE #0

Marc Wiz marc at wiz.com
Mon Dec 8 14:48:12 PST 2003

On Wed, Dec 03, 2003 at 06:03:50PM +1000, Kevin Fleming wrote:
> I've done numerous tests with dump and different buffer sizes etc, but the
> maximum speed I can read from disk is approximately 14MB/s (measured by
> iostat).
> cpio / tar etc can read from disk at over 30MB/s ..
> Dump seems to spawn children (presumably for better IO) - is it possible to
> tweak the number of children for better IO performance.
> I can write to my tape unit at a sustained 25MB/s (AIT-3 on an LVD
> interface), so I'm wasting tape and time.


try adding the following parameters -C 32 -b 60 to the dump command
line.  The 60 for the -b option was suggested to me by the dump
maintainer.  The 32 is 32 megabytes for the cache size.  I have 256
MB of memory so I figured 32 was good for me.  If you have more
memory you might want to experiment with a higher cache size.

Also make sure you RTFM the dump man page.

I don't know if either parameter is in the release you are running.

You might also want to consider piping the output of dump to dd and then
to the tape.  There has been plenty of discussions on many mailing
lists about speeding up dump with dd.


Marc Wiz
marc at wiz.com
Yes, that really is my last name.

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