[sclug] RAID stuff again

[Alex Butcher]

On Fri, 23 Sep 2005, Matt wrote:

> * Peter Brewer <p.w.brewer at reading.ac.uk> [2005-09-23 11:05:57]:
>> At the risk of boring everyone shitless with my infamous RAID - can
>> anyone tell me if my raid sync is unusually slow:
>>
>> md2 : active raid5 dm-15[7] dm-14[6] dm-13[5] dm-12[4] dm-11[3] dm-10[2]
>> dm-9[1] dm-8[0]
>>      1172101632 blocks level 5, 64k chunk, algorithm 2 [7/7] [UUUUUUU]
>>      [=======>.............]  resync = 36.9% (72197384/195350272)
>> finish=1969.9min speed=1040K/sec
>>
>> Am I falling victim to being a complete cheap scab re. controller and/or
>> disks?  Why on earth would it take the best part of 48 hours to sync a
>> 1.2Tb partition?
>
> It deliberately doesn't munch all of your disc I/O when it does this,
> when you started the rebuild, there was probably a kernel or syslog
> message stating the maximum speed it will rebuild at.
>
> You should be able to change the rate, but I don't remember how as I've
> never needed to.

It's tweakable by echo'ing into /proc/sys/dev/raid/speed_limit_max. The
units are KBytes/s. The default is documented as being 100,000KB/s, but it's
200,000KB/s here (and I'm sure I remember it being lower, too).

> Matt

Alex.
-- 
Alex Butcher      Brainbench MVP for Internet Security: www.brainbench.com
Bristol, UK                      Need reliable and secure network systems?
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