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How to Read IOmeter Disk IO Results

You ran IOmeter and produced your results file. NOW WHAT!?


There are a few things to do here. First, you can get a better sense of what the data means by loading the results CSV (copy&paste the raw text data, now from Excel) into this formatting tool:


Okay, great! So.. what do these numbers mean? The image below is the top portion of a report procedure at vmktree.org. It’s for an Dell MD3200 SAN that we believe is underperforming.


These numbers alone don’t mean much. Instead, you need to context.

  • Figure out the underlying disk storage. Is this a single SATA 2 disk? If so, it is theoretically capable of 300 MB/s. Note that a read cache and a write cache will both have a huge impact on these numbers. That said, if my results for a read a 10 Mb/s then something is wrong. A single disk should probably be pumping out read numbers around 60-80 MB/s.
  • Is the storage based on RAID? If so, what level of RAID? RAID-5 with no write caching is going to have worse write performance than RAID-10 with write caching for example. If I have several disk in a RAID-10 set, I’d like to see my read numbers for example in the 300 MB/s+ range. With good read caching I may hit 1000 Mb/s because of the tricks the storage system will play.
  • What about the block size for the testing? Bigger blocks tend to saturate the storage better so my throughput is faster on reads and writes. (Again, sometimes!)

Really, you need to compare your results to other people’s results. There is a well-read VMware community thread on this whole topic and it results in a spreadsheet to compare your storage against other people’s storage.



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