Reading from ZFS mirror 2x slower than expected?

[Bob Friesenhahn]

On Thu, 28 Jan 2010, Urmas Lett wrote:

> While reading from simple zfs mirror 'dd if=zfs.test of=/dev/null bs=512k' 
> systat -vm shows individual disks only 50% busy:

How big is the file 'zfs.test'?  How was it created?  If it was 
created from /dev/zero then its content is bogus.  You need to test 
with non-zero data.

It may be that zfs's prefetch is not working adequately.  With perfect 
prefetch, the read rate should be doubled.

Bob
--
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/