Testing Disk I/O Performance

[Jorge Cocomess]

Okay, I got it. Here's the latest test result.

time dd if=/dev/sdad1 of=/dev/null bs=8192 count=131072
131072+0 records in
131072+0 records out

real 0m7.541s
user 0m0.067s
sys 0m3.436s


Can you tell me how to convert these numbers?

Thanks much!

Jorge

[Ivan Ferreira]

Very simple. It took 0m7.541s to read 1 GB of data with a 8k block size, that is 1024MB/7.513=135,8 MB/s.

[Mike Stroyan]

Be careful to measure I/O activity that is representative of what you really care about. It can be tempting to measure things that are easy to measure, even though they are not actually the same activities that you really want use the system for. I do value simple benchmarks for their ability to bring clarity. But they can mislead if you if they don't bottleneck in the same ways as the actual application load. Differences in buffer size or read-ahead predictibility or many other factors can cause very different results.

[Jorge Cocomess]

Ivan,

So, what you're saying is that from the test result, it was 135 MB/s?

Thanks,
Jorge

[Jorge Cocomess]

Mike,

Thanks for your feedback. I am just trying to find a way to do the I/O comparison from the based test numbers before we migrate our DB from one SAN storage to another.

Thanks,
Jorge

[dirk dierickx]

using dd to measure io performance, you will only get a part of the true performance.
most disks will be able to read a sequence of data pretty fast, random access, write speeds etc are equally important.
that is why true benchmark tools are better suited.