From owner-freebsd-fs  Fri Sep 22  1:10:29 2000
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From: Soren Schmidt <sos@freebsd.dk>
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Subject: Re: disable write caching with softupdates?
In-Reply-To: <200009220757.e8M7vtG46023@netplex.com.au> from Peter Wemm at "Sep 22, 2000 00:57:55 am"
To: peter@netplex.com.au (Peter Wemm)
Date: Fri, 22 Sep 2000 10:13:13 +0200 (CEST)
Cc: Stephen.Byan@quantum.com (Stephen Byan),
	mbendiks@eunet.no ('Marius Bendiksen'), fs@FreeBSD.ORG,
	sos@FreeBSD.ORG, freeBSD-scsi@FreeBSD.ORG
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It seems Peter Wemm wrote:
> > Well, I have been toying a bit with this, so far results are just
> > timing of a make -j16 buildworld on two IBM DJNA drives (ie no tags)
> > with varius setups.
> > 
> > ATA driver "as is":
> > 3602.63 real         0.00 user      2865.62 sys
> > 
> > ATA driver with flush cache on "BIO_ORDERED":
> > 3964.18 real         0.00 user      2870.09 sys
> > 
> > ATA driver with write cache disabled:
> > 4423.30 real         0.00 user      2871.87 sys
> > 
> > So, having the write cache there definitly is a win.
> 
> It is a win only if you do not value your data.  I would gladly turn it off.
> How do we do this right now?   (ie: completely off)

Se the patch from yesterday, but I'llcome up with a better one (sysctl)
as soon as I get a few hours...

> > I'll try this on TWO IBM DTLA drives with tags enabled and see what gives..
> 
> I'm curious to know if tagged queueing compensates for the loss incurred by
> disabling write caching.

I'll know later today and will post my findings...

-Søren


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