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Old 10-04-2010, 06:47 PM   #1
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Calculating IOPS


Can anyone give me a help in calculating the IOPS for my system please?

I had understood that IOPS could be calculated by monitoring IOSTAT. The r/s (reads/sec) and w/s (write/sec) combined basically gave you the peak IOPS.

However having monitored iostat for my app during a performance test, the figures I'm seeing lead me to believe that iostat couldn't be a reliable way to calculate IOPS. I get values of over 10,000 for w/s! I didn't think this was possible given the storage system i have (4 x 7500rpm sata disks in raid 5).

Can anyone help me? How *should* I calculate IOPS? How could I get over 10 thousand writes per second? Is it cahcing?

Thanks for any help,
Old 10-05-2010, 05:47 PM   #2
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Depends how you define I/O. From the applications perspective, that is the rate its reads and writes are being serviced. So as a (logical) service rate, it has some validity. And yes, a perfect example of the benefits of caching.
There are benchmarks that will give you the performance of your system, but not for your own application. These use direct I/O to (deliberately) remove the caching from the equation.
blktrace is a block device driver tool that shows the actual I/O merging and subsequent physical I/O call. Now supports per-partition monitoring, so that might be an option if you have all your data on particular partition(s) - with no other files on those partitions(s).
There are user-land tools for it, but I haven't looked at it since it was beta code, so I'm not aware of the current status.


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