From owner-freebsd-fs  Thu Sep 21 14:20:37 2000
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From: Terry Lambert <tlambert@primenet.com>
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Subject: Re: disable write caching with softupdates?
To: archie@whistle.com (Archie Cobbs)
Date: Thu, 21 Sep 2000 21:20:00 +0000 (GMT)
Cc: mbendiks@eunet.no (Marius Bendiksen), sos@freebsd.org,
	fs@freebsd.org, terry@lambert.org
In-Reply-To: <200009211702.KAA13662@bubba.whistle.com> from "Archie Cobbs" at Sep 21, 2000 10:02:16 AM
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> > Please make this conditional, as people with non-crippled hardware might
> > want to employ the write cache. A sysctl or build option would be best.
> 
> Yep, that was what I was originally suggesting.
> 
> Soren do you want me to try to come up with a patch? 
> I don't claim to understand IDE technology.. can you
> just send the disable command at any time or is it
> more complicated than that?

I would also send a flush command.

I would be skeptical of an IDE drive perhaps disabling the cache,
and leaving the thing dirty.

Not knowing the exact details of when the cache control may be
changed, I can't say for sure (it may have to be done by the
BIOS at boot time, for all I know.

If you go over to my cube, there is a full technical specification
of the ATA stuff for the Quantum drives we used to use in the
InterJet II, prior to the IBM acquisition, and it has this
information in it, in detail.  Yung gave me the documentation
when Julian and I were trying to figure out how much DC holdup
was required after an AC failure for us to be able to ensure
that thee was no sector corruptions, and that the outstanding
operations on the drive were committed, after throwing a pin
into the soft updates clock to ensure that no more writes were
scheduled.

FWIW...


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.


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