Messages in this thread | | | Date | Fri, 6 Jul 2007 16:44:19 +0100 | From | "Daniel J Blueman" <> | Subject | Re: Understanding I/O behaviour |
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> > On 5 Jul, 16:50, Martin Knoblauch <spamtrap@knobisoft.de> wrote: > > > Hi, > > > > > > for a customer we are operating a rackful of HP/DL380/G4 boxes > > that > > > have given us some problems with system responsiveness under [I/O > > > triggered] system load. > > [snip] > > > > IIRC, the locking in the CCISS driver was pretty heavy until later in > > the 2.6 series (2.6.16?) kernels; I don't think they were backported > > to the 1000 or so patches that comprise RH EL 4 kernels. > > > > With write performance being really poor on the Smartarray > > controllers > > without the battery-backed write cache, and with less-good locking, > > performance can really suck. > > > > On a total quiescent hp DL380 G2 (dual PIII, 1.13GHz Tualatin 512KB > > L2$) running RH EL 5 (2.6.18) with a 32MB SmartArray 5i controller > > with 6x36GB 10K RPM SCSI disks and all latest firmware: > > > > # dd if=/dev/cciss/c0d0p2 of=/dev/zero bs=1024k count=1000 > > 509+1 records in > > 509+1 records out > > 534643200 bytes (535 MB) copied, 11.6336 seconds, 46.0 MB/s > > > > # dd if=/dev/zero of=/dev/cciss/c0d0p2 bs=1024k count=100 > > 100+0 records in > > 100+0 records out > > 104857600 bytes (105 MB) copied, 22.3091 seconds, 4.7 MB/s > > > > Oh dear! There are internal performance problems with this > > controller. > > The SmartArray 5i in the newer DL380 G3 (dual P4 2.8GHz, 512KB L2$) > > is > > perhaps twice the read performance (PCI-X helps some) but still > > sucks. > > > > I'd get the BBWC in or install another controller. > > > Hi Daniel, > > thanks for the suggestion. The DL380g4 boxes have the "6i" and all > systems are equipped with the BBWC (192 MB, split 50/50). > > The thing is not really a speed daemon, but sufficient for the task. > > The problem really seems to be related to the VM system not writing > out dirty pages early enough and then getting into trouble when the > pressure gets to high.
Hmm...check out /proc/sys/vm/dirty_* and the documentation in the kernel tree for this.
Just measuring single-spindle performance, it's still poor on RH EL4 (2.6.9) x86-64 with 64MB SmartArray 6i (w/o BBWC):
# swapoff -av swapoff on /dev/cciss/c0d0p2
# time dd if=/dev/cciss/c0d0p2 of=/dev/null bs=1024k count=1000 real 0m49.717s <-- 20MB/s
# time dd if=/dev/zero of=/dev/cciss/c0d0p2 bs=1024k count=1000 real 0m25.372s <-- 39MB/s
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