linux-kernel - Re: RAID extremely slow

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Message-ID: <5012E717.9070808@tmr.com>
Date:	Fri, 27 Jul 2012 15:08:07 -0400
From:	Bill Davidsen <davidsen@....com>
To:	Kevin Ross <kevin@...ilyross.net>,
	Linux RAID <linux-raid@...r.kernel.org>,
	Linux Kernel mailing List <linux-kernel@...r.kernel.org>
Subject: Re: RAID extremely slow

Kevin Ross wrote:
>
>>>
>>>> unused devices:<none>
>>>>
>>>> # cat /proc/sys/dev/raid/speed_limit_min
>>>> 10000
>>> MD is unable to reach its minimum rebuild rate while other system
>>> activity is ongoing.  You might want to lower this number to see if that
>>> gets you out of the stalls.
>>>
>>> Or temporarily shut down mythtv.
>>
>> I will try lowering those numbers next time this happens, which will probably
>> be within the next day or two.  That's about how often this happens.
>
> Unfortunately, it has happened again, with speeds at near zero.
>
> # cat /proc/mdstat
> Personalities : [raid6] [raid5] [raid4]
> md0 : active raid6 sdh1[0] sdd1[9] sde1[10] sdb1[6] sdi1[7] sdc1[4] sdf1[3]
> sdg1[8] sdj1[1]
>        6837311488 blocks super 1.2 level 6, 512k chunk, algorithm 2 [9/9]
> [UUUUUUUUU]
>        [=>...................]  resync =  8.3% (81251712/976758784)
> finish=1057826.4min speed=14K/sec
>
> unused devices: <none>
>
> atop doesn't show ANY activity on the raid device or the individual drives.
> http://img687.imageshack.us/img687/2913/screenshotfrom201207252.png
>
> Also, I tried writing to a test file with the following command, and it hangs.
> I let it go for about 30 minutes, with no change.
>
> # dd if=/dev/zero of=test bs=1M count=1
>
> dmesg only reports hung tasks.  It doesn't report any other problems. Here's my
> dmesg output:
> http://pastebin.ca/2174778
>
> I'm going to try rebooting into single user mode, and see if the rebuild
> succeeds without stalling.
>
Have you set the io scheduler to deadline on all members of the array? That's 
kind of "job one" on older kernels.

-- 
Bill Davidsen <davidsen@....com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot


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