linux-kernel - Re: Understanding I/O behaviour

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Date:	Fri, 6 Jul 2007 15:25:16 +0100
From:	"Daniel J Blueman" <daniel.blueman@...il.com>
To:	"Martin Knoblauch" <spamtrap@...bisoft.de>
Cc:	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: Understanding I/O behaviour

On 5 Jul, 16:50, Martin Knoblauch <spamtrap@...bisoft.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.

Daniel
-- 
Daniel J Blueman
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