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http://sebastien.godard.pagesperso-orange.fr/man_iostat.html this is iostat manual page, we can learn about:

%util

Percentage of CPU time during which I/O requests were issued to the device (bandwidth utilization for the device). Device saturation occurs when this value is close to 100% for devices serving requests serially. But for devices serving requests in parallel, such as RAID arrays and modern SSDs, this number does not reflect their performance limits.

who can explain it? thanks.

lyush
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1 Answers1

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Marc Brooker provides a good explanation on his blog:

http://brooker.co.za/blog/2014/07/04/iostat-pct.html

In summary:

When iostat says %util, it means "Percentage of CPU time during which I/O requests were issued to the device". The percentage of the time the drive was doing at least one thing. If it's doing 16 things at the same time, that doesn't change. Once again, this calculation works just fine for magnetic drives (and Jane), which do only one thing at a time. The amount of time they spend doing one thing is a great indication of how busy they really are. SSDs (and RAIDs, and Alice), on the other hand, can do multiple things at once. If you can do multiple things in parallel, the percentage of time you're doing at least one thing isn't a great predictor of your performance potential.

JamieL
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  • hi, what if there are 15-to-20 blocked processes(column 'b') and 35 in '`wa`' columns of `vmstat 1` output for hardware raid with %util=100%. Does this mean the IO is saturated – sherpaurgen Oct 09 '18 at 05:22