On Sunday 23 November 2008, Greg Freemyer wrote:
On Sun, Nov 23, 2008 at 6:52 AM, peter nikolic
wrote:
First 83 MB/sec is about 5GB a minute. That is a very respectable speed, but I can see why you would like to get 112 MB/s, which would be about 6.5 GB a minute.
Hard to say what is going on, but a few issues with your benchmark.
1) /dev/zero in 11.0 (iirc) is buggy and causes performance limitations. Should not be used for bench mark purposes, especially at speed as high as you are getting.
2) Inner radius of the physical drive will transmit at a different speed than outer radius. iirc, the outer radius is faster because the RPMs are the same, but they pack more data onto the outer tracks than they do on the inner tracks so you get more data per revolution.
Since you are writing to a file, you don't have anyway to say what part of the drive you are writing to. And yes, the variation can be pretty big. Try performing your process to an entire drive (dd if=/dev/zero of=/dev/sdb ...) And then use iostat -d 5 to watch the transfer speed. Assuming /dev/zero is not limiting you, you should see the transfer rate slowly decrease as you continue writing data.
3) You don't say if it is the same filesystem / PCI-bus / cabling / disk controller / etc. At 100MB/sec you are really pushing all of the components hard.
4) A 1 GB test is way to small to mean much. Lots of caches involved that can interfere with that small of a test. ie. If your disk has a 256MB write cache, it will report done when you're really only 75% done. Kernel cache can be even bigger. Add them together and is is very conceivable that well over half of your 15 second test is just pushing data to cache, and it is taking another 15 seconds to flush those caches. Thus in reality you are only getting half the speed you think you are.
Good luck tracking in down, but I suspect it is much more of a complex issue to even benchmark than you suspect.
Greg -- Greg Freemyer Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer First 99 Days Litigation White Paper - http://www.norcrossgroup.com/forms/whitepapers/99%20Days%20whitepaper.pdf
The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com
Hi . I suspect it is something to do with the last kernel update i had never noticed it slow before the last kernel update it gets that bad at times it causes the music to actually pause briefley , reacon it is going to take a bit of hunting down noticed i got the Mobo wrong it is an 939A8X-M still Asrock i have never had any problems with them so stick with what woks Cheers Pete still hunting -- SuSE Linux 10.3-Alpha3. (Linux is like a wigwam - no Gates, no Windows, and an Apache inside.) -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org