RAID Performance

CHUNK

Calculate the chunk size by using iostat

#iostat -x

Device:         rrqm/s   wrqm/s   r/s   w/s             rsec/s   wsec/s    avgrq-sz avgqu-sz   await  svctm  %util
dm-0              0.00     0.00       0.00 4548.51     0.00 36388.12    40.00   203.91       44.83   0.02  10.69
Take the average request size and times it by 512 then divide by the amount of disks in the RAID array. So if you have a raid 5 with three disks you would divide by 2 as one of the disks is for parity, for example

(40*512)/1024/2=10
So the optimum chucnk size for this would be 8K because you always round down to the nearest 2 to the power. You can create the array with this chunk witht he following commamd

#mdadm -C /dev/md1 -l5 -n3 --chunk=8/dev/sd[def] -a yes


STRIDE
The optimum stride is calculated using chunk divided by block size so for the above array it will be

8/4=2

mke2fs -j -b 4096 -E stride=2 /dev/md1