Re: Slow RAID Check/high %iowait during check after updgrade from CentOS 6.5 -> CentOS 7.2

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On 2016-05-25 19:13, Kelly Lesperance wrote:
> Hdparm didn’t get far:
> 
> [root@r1k1 ~] # hdparm -tT /dev/sda
> 
> /dev/sda:
>  Timing cached reads:   Alarm clock
> [root@r1k1 ~] #

Hi Kelly,

Try running 'iostat -xdmc 1'. Look for a single drive that has
substantially greater await than ~10msec. If all the drives 
except one are taking 6-8msec, but one is very much more, you've
got a drive that drags down the whole array's performance.

Ignore the very first output from the command - it's an
average of the disk subsystem since boot.

Post a representative output along with the contents /proc/mdstat.

Good luck,
-- 
Charles Polisher

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