Re: scsi vs ide performance on fsync's

Mike Black
2001-03-06T13:51:12Z

Write caching is the culprit for the performance diff:

On IDE:
time xlog /blah.dat fsync
0.000u 0.190s 0:01.72 11.0% 0+0k 0+0io 91pf+0w
# hdparm -W 0 /dev/hda

/dev/hda:
setting drive write-caching to 0 (off)
# time xlog /blah.dat fsync
0.000u 0.220s 0:50.60 0.4% 0+0k 0+0io 91pf+0w
# hdparm -W 1 /dev/hda

/dev/hda:
setting drive write-caching to 1 (on)
# time xlog /blah.dat fsync
0.010u 0.230s 0:01.88 12.7% 0+0k 0+0io 91pf+0w

On my SCSI setup:
# time xlog /usr5/blah.dat fsync
0.020u 0.230s 0:30.48 0.8% 0+0k 0+0io 91pf+0w

________________________________________
Michael D. Black Principal Engineer
mblack@csihq.com 321-676-2923,x203
http://www.csihq.com Computer Science Innovations
http://www.csihq.com/~mike My home page
FAX 321-676-2355
----- Original Message -----
From: "Andre Hedrick" <andre@linux-ide.org>
To: "Linus Torvalds" <torvalds@transmeta.com>
Cc: "Douglas Gilbert" <dougg@torque.net>; <linux-kernel@vger.kernel.org>
Sent: Tuesday, March 06, 2001 2:12 AM
Subject: Re: scsi vs ide performance on fsync's

On Mon, 5 Mar 2001, Linus Torvalds wrote:

> Well, it's fairly hard for the kernel to do much about that - it's almost
> certainly just IDE doing write buffering on the disk itself. No OS
> involved.

I am pushing for WC to be defaulted in the off state, but as you know I
have a bigger fight than caching on my hands...

> I don't know if there is any way to turn of a write buffer on an IDE disk.

You want a forced set of commands to kill caching at init?

Andre Hedrick
Linux ATA Development
ASL Kernel Development
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