Re: RAID 10 Benchmark with different I/O schedulers (was: Performance increase with elevator=deadline)

On May 5, 2008, at 7:33 PM, Craig James wrote:

> I had the opportunity to do more testing on another new server to
> see whether the kernel's I/O scheduling makes any difference.
> Conclusion: On a battery-backed RAID 10 system, the kernel's I/O
> scheduling algorithm has no effect. This makes sense, since a
> battery-backed cache will supercede any I/O rescheduling that the
> kernel tries to do.
>

this goes against my real world experience here.

> pgbench -i -s 20 -U test
> pgbench -c 10 -t 50000 -v -U test
>

You should use a sample size of 2x ram to get a more realistic number,
or try out my pgiosim tool on pgfoundry which "sort of" simulates an
index scan. I posted numbers from that a month or two ago here.

--
Jeff Trout <jeff(at)jefftrout(dot)com>
http://www.stuarthamm.net/
http://www.dellsmartexitin.com/