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

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,