Re: Where is the performance bottleneck?

[Holger Kiehl <Holger.Kiehl@dwd.de>]

On Wed, 31 Aug 2005, Vojtech Pavlik wrote:

> On Tue, Aug 30, 2005 at 08:06:21PM +0000, Holger Kiehl wrote:
> > > > How does one determine the PCI-X bus speed?
> > >
> > > Usually only the card (in your case the Symbios SCSI controller) can
> > > tell. If it does, it'll be most likely in 'dmesg'.
> > There is nothing in dmesg:
> >
> >    Fusion MPT base driver 3.01.20
> >    Copyright (c) 1999-2004 LSI Logic Corporation
> >    ACPI: PCI Interrupt 0000:02:04.0[A] -> GSI 24 (level, low) -> IRQ 217
> >    mptbase: Initiating ioc0 bringup
> >    ioc0: 53C1030: Capabilities={Initiator,Target}
> >    ACPI: PCI Interrupt 0000:02:04.1[B] -> GSI 25 (level, low) -> IRQ 225
> >    mptbase: Initiating ioc1 bringup
> >    ioc1: 53C1030: Capabilities={Initiator,Target}
> >    Fusion MPT SCSI Host driver 3.01.20
> >
> > > To find where the bottleneck is, I'd suggest trying without the
> > > filesystem at all, and just filling a large part of the block device
> > > using the 'dd' command.
> > >
> > > Also, trying without the RAID, and just running 4 (and 8) concurrent
> > > dd's to the separate drives could show whether it's the RAID that's
> > > slowing things down.
> > Ok, I did run the following dd command in different combinations:
> >
> >    dd if=/dev/zero of=/dev/sd?1 bs=4k count=5000000
>
> I think a bs of 4k is way too small and will cause huge CPU overhead.
> Can you try with something like 4M? Also, you can use /dev/full to avoid
> the pre-zeroing.
Ok, I now use the following command:

      dd if=/dev/full of=/dev/sd?1 bs=4M count=4883

Here the results for all 8 disks in parallel:

      /dev/sdc1 24.957257 MB/s
      /dev/sdd1 25.290177 MB/s
      /dev/sde1 25.046711 MB/s
      /dev/sdf1 26.369777 MB/s
      /dev/sdg1 24.080695 MB/s
      /dev/sdh1 25.008803 MB/s
      /dev/sdi1 24.202202 MB/s
      /dev/sdj1 24.712840 MB/s

A little bit faster but not much.

Holger

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