Sample Question - Need help

[timevisser]

Here is a sample test question I have tried to find a good way to figure out the answer but have not been able to.  I am missing something.

Q.  # of IOPS to limit disk throughput to 20 MBps if application writes 128KB blocks. 

In a recent interview I had this type of question was asked and I said I did not know how.  I still do not.  How do you do the calculations for this?  What is the answer?  Any good articles that explain this well?  I have looked at the following documents but they did not help.

Calculate IOPS in a storage array - TechRepublic

http://www.vmware.com/files/pdf/products/vsphere/VMware-vSphere-Evaluation-Guide-2-Advanced-Storage....

http://kb.vmware.com/selfservice/microsites/search.do?cmd=displayKC&docType=kc&externalId=1031773&sl...

VMware vSphere 5.1

[a_p_]

Take a look at http://en.wikipedia.org/wiki/IOPS which explains how to calculate this.

André

[timevisser]

Andre, thanks for the new URL to read.  The formula there is IOPS * TransfersizeinBytes = BytesPerSec.  The question is trying to figure out the number of IOPS.  How do you determine the number of IOPS based on 20 MBps with writing 128KB blocks? 

[timevisser]

Do you take the throughput divide it by # of blocks.  So in this example, 20 / 128 = .156 or 156 IOPS?

[a_p_]

20 MBps = 20,000,000 Bytes per second

128KB = 128,000 Bytes

With the formula IOPS * TransfersizeinBytes = BytesPerSec that's IOPS = BytesPerSec / TransfersizeinBytes

--> 20,000,000 / 128,000 = 156,25

André

[timevisser]

Thanks Andre!!!  It makes sense now.