Formula for calculating IOPS ?

Question

Hi,

I am trying to figure out how many disks are required by our Storage Array. I find a number of web site mentioning how to calculate IOPS. However, it seems that they use different formulas. I just wonder which one is the correct one for me to use (OR maybe I just my misunderstanding / calculation error).

First Formula

http://www.yellow-bricks.com/2009/12/23/iops/

Raw IOPS = (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

Second Formula

http://theithollow.com/2012/03/21/understanding-raid-penalty/

Functional IOPS = (Raw IOPS * Write % / RAID Penalty) + (RAW IOPS * Read %)

If Raw IOPS is 2800 (Calculation from First Formula),Total IOPS (i.e. Functional IOPS) will be = (2800 x 0.4) + ((2800 x 0.6) / 4) = 1540 IOPs.

Your advice is sought.

Thanks

dynamox · Answer

first formula take host iops , read/write ratio and tells you how much backend iops will be generated. Your second formula looks odd, that website takes a number of drives and based on read/write ratio tells you how many host iops it will be able to service.

Take a look at this discussion, RRR and Jon explain performance calculations in great details

https://community.emc.com/thread/148025

RRR · Answer

As Dynamox pointed out our 'Ask the Expert' discussion is a good source of how to do these calculations. If you have questions after reading the discussion, ask! Feel free to join the discussion.

VNX

Formula for calculating IOPS ?

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