From owner-freebsd-mobile  Wed Mar 14  6:10:34 2001
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From: Soren Schmidt <sos@freebsd.dk>
Message-Id: <200103141410.PAA29652@freebsd.dk>
Subject: Re: Disk I/O problem in 4.3-BETA
In-Reply-To: <200103141405.f2EE5Ks71827@aslan.scsiguy.com> from "Justin T. Gibbs" at "Mar 14, 2001 07:05:20 am"
To: gibbs@scsiguy.com (Justin T. Gibbs)
Date: Wed, 14 Mar 2001 15:10:10 +0100 (CET)
Cc: bright@wintelcom.net (Alfred Perlstein),
	Helge.Oldach@de.origin-it.com (Helge Oldach), oberman@es.net,
	mobile@FreeBSD.ORG, stable@FreeBSD.ORG
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It seems Justin T. Gibbs wrote:
> >First off, some disk caches are getting > 10megs, that's a lot
> >of potnetial seeking after loosing power depending on the cache
> >contents...
> 
> I've heard that most modern drives reserve a contiguous area of the
> disk the size of the cache near where the heads park to dump any
> cache contents on power outage.  This avoids most if not all seeking.
> When the disk powers up again, the reserve track is read and the
> transactions are written to the correct locations.  Any disk that does
> this should be safe to use with write caching enabled.

I belived that as well, but after consulting with some of the
disk vendors, I found out this was just wishfull thinking, almost
noone does this anymore infact only one remembered a single
drive that did this...

-Søren

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