[CentOS] measuring iops on linux - numbers make sense?

Amos Shapira amos.shapira at gmail.com
Fri Dec 4 21:57:55 UTC 2009


When approaching hosting providers for services, the first question
many of them asked us was about the amount of IOPS the disk system
should support.

While we stress-tested our service, we recorded between 4000 and 6000
"merged io operations per second" as seen in "iostat -x" and collectd
(varies between the different components of the system, we have a few
such servers).

A couple of hosting providers told us that this (iostat and collectd
"merged operations per second") is a not so bad way to get IOPS.

A partner of ours doubts that this is possible with the current
hardware - a 3ware 9690SA-4I4E
(http://www.3ware.com/products/sas-9690SA.asp) with 512Mb battery
backed up cache and 8 SAS 15k rpm disks (SEAGATE ST3300656SS) in RAID
1+0. They calculate 750 IOPS per spindle and say that the maximum they
ever saw from any 15k disk was 350 iops on RAID 0.

Am I measuring the numbers correctly? Is there a better way to measure
IOPS on CentOS?

The OS is CentOS 5.3 x86_64, the rest of the hardware is 64Gb RAM, 2
quad-core 3GHz Intel Xeon CPU's.



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