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

Wed May 25 21:43:25 UTC 2016
cpolish at surewest.net <cpolish at surewest.net>

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