RE: I/O performance
- From: "Allen, Brandon" <Brandon.Allen@xxxxxxxxxxx>
- To: "ChrisDavid.Taylor@xxxxxxxxxxxxxxx" <ChrisDavid.Taylor@xxxxxxxxxxxxxxx>, "'niall.litchfield@xxxxxxxxx'" <niall.litchfield@xxxxxxxxx>, 'ORACLE-L' <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 8 Jun 2012 18:26:18 +0000
I think the 75% estimate is a good rule of thumb, but I don't think the
explanation below is correct. I think if you run a test of only single-block
random reads, you can indeed hit the calculated max IOPS of a disk drive. I
think the reason for reducing the IOPS estimate to 75% for actual
implementation planning is that in real-world usage many of the IOs will
probably be larger sequential IOs (rather than random IOs), e.g. Full Table
Scans, which will increase the observed transfer rate, but decrease the IOPS.
Notice that I've prefaced all my statements with "I *think*" - that's because I
haven't actually tested these claims myself and I'm not a hardware expert, so
feel free to correct me if I'm wrong.
Regards,
Brandon
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Taylor, Chris David
Of the approximate calculated IOPS, you can only count on about 75% of that
capacity as you will never reach the full calculated IOPS because there is a
direct relationship between disk utilization and response time - as utilization
increases, response time decreases, so only count on about 75% of the
calculated IOPS per disk. (I tried to find a specific link illustrating this
relationship but gave up)
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