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Date:      Wed, 7 Mar 2001 20:06:13 -0600
From:      Mike Meyer <mwm@mired.org>
To:        "Philip J. Koenig" <pjklist@ekahuna.com>
Cc:        questions@freebsd.org
Subject:   Re: SoftUpdates/hardware write cache
Message-ID:  <15014.59669.718668.654739@guru.mired.org>
In-Reply-To: <123006805@toto.iv>

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Philip J. Koenig <pjklist@ekahuna.com> types:
> Apparently the new drive has the internal write cache turned off by 
> default.  I'm about to enable SoftUpdates with the tunefs thing and I 
> was wondering if I should also enable the disk's internal write 
> cache.  My experience in the past with other OS's says it can make a 
> big performance improvement.

Generally, this isn't recommended. Soft updates *depend* on the device
actually having written the data to disk when it claims it has, and in
the order it specified.

> This machine runs on a large UPS so power-loss isn't a big issue.

Well, if you want to try it, go ahead. If you have the time, I'd be
interested in timings for all four cases (softupdates yes/no, write
cache yes/no).

> I know there is some Unix program that can at least read mode pages, 
> I'm hoping it can set them too.  My DOS program won't work on this 
> hardware and I'd hate to have to stick the drive on a Windows machine 
> to set that setting. :-)

Camcontrol can do that for your scsi devices.

	<mike
--
Mike Meyer <mwm@mired.org>			http://www.mired.org/home/mwm/
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.

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