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SubjectRe: Linux i/o tweaking
On Thu, Nov 15 2001, Roy Sigurd Karlsbakk wrote:
> Hi all
> After three days at Compaq's lab in Oslo, testing their medium-level
> servers and storage systems with Linux, I've come to some sort of
> conclusions, although these may be wrong. I also have come over a few
> problems that I couln't find a good solution to.
> * When running RAID from a Compaq Smart 5302/64 controller, software
> RAID-5 is (slightly - ~15%) faster (on JBOD - each disk is configured as
> a RAID-0 device with max - 256kB - stripe size) than the
> hardware/controller based RAID-5. Both CPUs (1266MHz/512kB cache) are
> maxed out by reading from software RAID-5 (???), giving me >= 107MB/s on
> two SCSI-3 buses with six disks on each bus.
> * Even though I can get up to 25 MB/s from each disk, I can't get more
> than 107 MB/s on the whole bunch (12 drives). It doesn't help much to do
> RAID-0 either. Don't understand anything ...

Could you please try and profile where the time is spent? Boot with
profile=2, and then do

# readprofile -r
# do I/O testing
# readprofile | sort -nr

Jens Axboe

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