Storage IO Calculation - Basics

YellowBricks - IOPs?
Calculate IOPS in a storage array
Excellent White Paper explaining resources sizing in VDI environment
Calculating Disk Usage using Diskmon
New !! Open unofficial storage performance thread

Avg IOPs:
7200 RPM - 75
10K RPM - 125
15K RPM - 175

RAID penalty:
Raid 0 : R=1, W=1
Raid 1 and 10 : R=1, W=2
Raid 5 : R=1, W=4
Raid 6 : R=1, W=6


Below quote from Yellow bricks

So how do we factor this penalty in? Well it’s simple for instance for RAID-5 for every single write there are 4 IO’s needed. That’s the penalty which is introduced when selecting a specific RAID type. This also means that although you think you have enough spindles in a single RAID Set you might not due to the introduced penalty and the amount of writes versus reads.

I found a formula and tweaked it a bit so that it fits our needs:

(TOTAL IOps × % READ)+ ((TOTAL IOps × % WRITE) ×RAID Penalty)

So for RAID-5 and for instance a VM which produces 1000 IOps and has 40% reads and 60% writes:

(1000 x 0.4) + ((1000 x 0.6) x 4) = 400 + 2400 = 2800 IO’s

The 1000 IOps this VM produces actually results in 2800 IO’s on the backend of the array, this makes you think doesn’t it?