On 03/20/2014 02:12 AM, Jeff Allison wrote:

The gist of my question is what kind of resync speed should I expect?

I have a HP N54L Microserver running centos 6.5.

In this box I have a 3x2TB disk raid 5 array, which I am in the
process of extending to a 4x2TB raid 5 array.

I've added the new disk --> mdadm --add /dev/md0 /dev/sdb

And grown the array --> mdadm --grow /dev/md0 --raid-devices=4

Now the problem the resync speed is v slow, it refuses to rise above
5MB, in general it sits at 4M.

Per second?

from looking at glances it would appear that writing to the new disk
is the bottle neck, /dev/sdb is the new disk.

Disk I/O In/s Out/s
md0 0 0
sda1 0 0
sda2 0 1K
sdb1 3.92M 0
sdc1 24.2M 54.7M
sdd1 11.2M 54.7M
sde1 16.3M 54.7M

Could you please send output of 'iostat -xm 1'? Also, do you anything in 
'top' that takes 100% CPU?

Thanks,
Bernd