On Wed, 31 Aug 2005, Vojtech Pavlik wrote:

On Tue, Aug 30, 2005 at 08:06:21PM +0000, Holger Kiehl wrote:

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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

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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