On Jan 28, 2008 11:25 AM, Ciro Iriarte <[EMAIL PROTECTED]> wrote: > Hi, anybody has some notes about tuning md raid5, lvn and xfs?. I'm > getting 20mb/s with dd and I think it can be improved. I'll add config > parameters as soon as i get home. I'm using md raid5 on a motherboard > with nvidia sata controller, 4x500gb samsung sata2 disks and lvm with > OpenSUSE [EMAIL PROTECTED] > > Regards, > Ciro > --
I have not done any raid 5 perf. testing: 20 mb/sec seems pretty bad, but not outrageous I suppose. I can get about 4-5GB/min from new sata drives. So about 75 MB/sec from a single raw drive (ie. dd if=/dev/zero of=/dev/sdb bs=4k) You don't say how your invoking dd. The default bs is only 512 bytes I think and that is totally inefficient with the linux kernel. I typically use 4k which maps to what the kernel uses. ie. dd if=/dev/zero of=big-file bs=4k count=1000 should give you a simple but meaningful test.. I think the default stride is 64k per drive, so if your writing 3x 64K at a time, you may get perfect alignment and miss the overhead of having to recalculate the checksum all the time. As another data point, I would bump that up to 30x 64K and see if you continue to get speed improvements. So tell us the write speed for bs=512 bs=4k bs=192k bs=1920k And the read speeds for the same. ie. dd if=big-file of=/dev/null bs=4k, etc. I would expect the write speed to go up with each increase in bs, but the read speed to be more or less constant. Then you need to figure out what sort of real world block sizes your going to be using. Once you have a bs, or collection of bs sizes that match your needs, then you can start tuning your stack. 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 -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
