On Wed, 1 Feb 2012, Jan Hellevik wrote:

Are all of the disks the same make and model?

They are different makes - I try to make pairs of different brands to minimise 

Does your pairing maintain the same pattern of disk type across all the pairings?

Some modern disks use 4k sectors while others still use 512 bytes. If the slow disk is a 4k sector model but the others are 512 byte models, then that would certainly explain a difference.

Assuming that a couple of your disks are still unused, you could try replacing the suspect drive with an unused drive (via zfs command) to see if the slowness goes away. You could also make that vdev a triple-mirror since it is very easy to add/remove drives from a mirror vdev. Just make sure that your zfs syntax is correct so that you don't accidentally add a single-drive vdev to the pool (oops!). These sorts of things can be tested with zfs commands without physically moving/removing drives or endangering your data.

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