On Fri, 27 Jul 2012 14:45:18 -0700, you wrote:

On 07/27/2012 12:08 PM, Bill Davidsen wrote:

quoted

Have you set the io scheduler to deadline on all members of the array? 
That's kind of "job one" on older kernels.

I have not, thanks for the tip, I'll look into that now.

Plus I disable the on-drive queuing (NCQ) during startup, right now 
I don't have benchmarks to show the difference.  This on a six by 1TB 
drive RAID6 array I built over a year ago on Slackware64-13.37:

# cat /etc/rc.d/rc.local
...
# turn off NCQ on the RAID drives by adjusting queue depth to 1
n=1
echo "rc.local: Disable RAID drives' NCQ"
for d in a b c d e f
do
        echo "  set NCQ depth to $n on sd${d}"
        echo $n > /sys/block/sd${d}/device/queue_depth
done
...

Maybe you could try that?  See if it makes a difference.  My drives 
are Seagate.

Grant.