Re: disk i/o performance problem
On Thu, May 31, 2007 at 11:02:06PM -0400, WHIRLYCOTT wrote:
> Etch: (output of hdparm)
>
> /dev/sda:
> Timing cached reads: 1588 MB in 2.00 seconds = 794.41 MB/sec
> Timing buffered disk reads: 176 MB in 3.03 seconds = 58.15 MB/sec
> CentOS: (output of hdparm)
>
> /dev/sda:
> Timing cached reads: 4480 MB in 2.00 seconds = 2242.86 MB/sec
> Timing buffered disk reads: 176 MB in 3.03 seconds = 58.16 MB/sec
The buffered disk reads are the same since that's the transfer rate from
the drive's buffer. The problem is the cache reads which is the time
from you OS's cache.
What does vmstat show as cache size with both OSs? Does one OS have
more processes going than the other? What happens if you boot up each
in init=/bin/sh, mount whatever filesystem holds hdparm ro, and run the
timing tests that way with only those few proceses running?
Finally, benchmarks are all well and good but how does this impact you
directly? What do you do that relies on fast cache disk IO for which
you end up waiting?
Doug.
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