linux-kernel - Re: RAID extremely slow

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Message-ID: <8oq618ldps0ijt76cr3k6vovkksm4b9vsb@4ax.com>
Date:	Sat, 28 Jul 2012 14:45:31 +1000
From:	Grant Coady <gcoady.lk@...il.com>
To:	Kevin Ross <kevin@...ilyross.net>
Cc:	Bill Davidsen <davidsen@....com>,
	Linux RAID <linux-raid@...r.kernel.org>,
	Linux Kernel mailing List <linux-kernel@...r.kernel.org>
Subject: Re: RAID extremely slow

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

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