N-way mirror read speedup in zfsonlinux

[Martin Matuška]

Hi everyone,

zfsonlinux has implemented a change in the N-way mirror device selection
algorithm by selecting the device with the least pending I/O instead of
random selection. They measured an increased read bandwidth increase up to
50% and IOPS increase up to 10%.

this might be useful for common ZFS code and we might consider porting this
to illumos and FreeBSD:
https://github.com/zfsonlinux/zfs/issues/1461
https://github.com/zfsonlinux/zfs/commit/556011dbec2d10579819078559a77630fc559112

Cheers,
mm