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Posted Monday, July 6, 2009 9:41 AM
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We are looking at purchasing a SAN therefore i am beginning to gather some stats to help with the storage/capacity planning.

I am currently using perfmon to retrieve disk reads/sec and disk writes/sec to discover how many IOPS our database server is doing.

However I have read in text books and on the web that to work out the current ops per disk depending on RAID levels I would need to use the following formulas:

operations per disk = (reads + (2 * writes)) / 2
RAID 10:
operations per disk = (reads + (2 * writes)) / number of disks

A sample of data at a certain time from one of our drives that is a RAID 10 of 4 disks is:

disk read/sec = 2939 and disk write/sec = 480

So to find the IOPS placed on each disk at that time would i simply do:

(2939 + (2 * 480) / 4
= 975 IOPS

And then to figure out how many disks i ideally need given they do roughly 180 IOPS would i use the following formula:

(2939 + (2 * 480) /180
= 22 disks

I would appreciate any feedback, comments on this to point me in the right direction.

Thanks in advance
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