David Wragg wrote:
I've not done anything different this time from when I created the original 
(512b)  pool. How would I check ashift?

For a zpool called "export"...

# zdb export | grep ashift
ashift: 12

As far as I know (although I don't have any WD's), all the current 4k sectorsize hard drives claim to be 512b sectorsize, so if you didn't do anything special, you'll probably have ashift=9.

I would look at a zpool iostat -v to see what the IOPS rate is (you may have bottomed out on that), and I would also work out average transfer size (although that alone doesn't necessarily tell you much - a dtrace quantize aggregation would be better). Also check service times on the disks (iostat) to see if there's one which is significantly worse and might be going bad.

Andrew Gabriel
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