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Date: Sun, 7 Jan 2007 21:30:46 -0600
From: Dan Nelson <dnelson@allantgroup.com>
To: David Gilbert <dgilbert@dclg.ca>
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Cc: freebsd-hackers@freebsd.org
Subject: Re: dump reads more than restore writes?
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In the last episode (Jan 07), David Gilbert said:
> I've got a command line like the following:
> 
> dump -0af - /dev/ad1s1g | restore -rf -
> 
> ... and I'm watching gstat.  ad1s1g is not mounted.  The disk on which
> the restore is running is also quiet (nobody using the disk).
> 
> And gstat says that ad1 is consistently reading 31 to 37 megabytes
> per second and ad2 (the restore disk) is consistently writing 10 to
> 13 megabytes per second.  This is over hours --- the figures never
> catch up.

If you have a lot of small files, dump may be rereading directory
information.  Dump has a cache option that can help, but make sure you
also dump a snapshot (i.e. always use -L when using -C).

-- 
	Dan Nelson
	dnelson@allantgroup.com