On Tue, Oct 02, 2007 at 03:56:17PM -0400, Ross S. W. Walker wrote: > Pasi Kärkkäinen wrote: > > > > On Tue, Oct 02, 2007 at 08:57:28PM +0300, Pasi Kärkkäinen wrote: > > > On Tue, Oct 02, 2007 at 09:39:09AM -0400, Ross S. W. Walker wrote: > > > > Simon Banton wrote: > > > > > > > > > > At 12:30 +0200 2/10/07, matthias platzer wrote: > > > > > > > > > > > >What I did to work around them was basically switching > > to XFS for > > > > > >everything except / (3ware say their cards are fast, > > but only on > > > > > >XFS) AND using very low nr_requests for every blockdev > > on the 3ware > > > > > >card. > > > > > > > > > > Hi Matthias, > > > > > > > > > > Thanks for this. In my CentOS 5 tests the nr_requests > > turned out by > > > > > default to be 128, rather than the 8192 of CentOS 4.5. > > I'll have a go > > > > > at reducing it still further. > > > > > > > > Yes, the nr_requests should be a realistic reflection of what the > > > > card itself can handle. If too high you will see io_waits stack up > > > > high. > > > > > > > > 64 or 128 are good numbers, rarely have I seen a card > > that can handle > > > > a depth larger then 128 (some older scsi cards did 256 I think). > > > > > > > > > > Hmm.. let's say you have a linux software md-raid array made of sata > > > drives.. what kind of nr_request values you should use for > > that for optimal > > > performance? > > > > > > > Or let's put it this way: > > > > You have a md-raid array on dom0. What kind of nr_requests > > values should you > > use for normal 7200 rpm sata-ncq disks on intel ich8 (ncq) > > controller? > > > > And then this md-array is seen as xvdb by domU.. what kind of > > nr_requests > > values should you use in domU? > > > > io-scheduler/elevator should be deadline in domU I assume.. > > how about in > > dom0? deadline there too? > > Arrr, where thou go thar be monsters... > > You got me Pasi, with Xen as the workload it adds a whole new > dimension. > > Unless you have hardware RAID, stick to the default setting > and when you see a bottleneck double check your hardware > drivers and RAID config first and only twiddle the queue > settings if everything else has been twiddled first. >
OK. I'm seeing quite high io-wait times on domU, but hardly any io-wait in dom0.. so I was wondering if I have too high nr_requests on domU. I think it is 256 atm. Maybe I'll have to do some benchmarking. What's the best multi-threaded / multi-process io-benchmark utility that works with filesystems instead of raw devices? and can read/write multiple files at once.. -- Pasi _______________________________________________ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
