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

On Sat, Dec 05, 2009 at 08:57:55AM +1100, Amos Shapira wrote:
> Hello,
> 
> 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.

I typically would look at the tps numbers (either in iostat or sar -b).
You might also be able to use blktrace output (combined with
seekwatcher) to generate IOPS data.

Someone out there may have some better suggestions.

Ray