From owner-freebsd-hackers  Thu Jun 18 20:36:25 1998
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From: Wilko Bulte <wilko@yedi.iaf.nl>
Message-Id: <199806182231.AAA05620@yedi.iaf.nl>
Subject: Re: Disk Cache
In-Reply-To: <Pine.BSF.3.96.980618173600.17695A-100000@super-g.inch.com> from spork at "Jun 18, 98 05:44:10 pm"
To: spork@super-g.com (spork)
Date: Fri, 19 Jun 1998 00:31:04 +0200 (CEST)
Cc: hackers@FreeBSD.ORG
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As spork wrote...

> I have a question about FBSD's disk cache mechanism.  What happens when
> you run a SCSI-SCSI raid controller that contains it's own cache memory?
> The kernel has no way of knowing that some things are already cached out
> beyond the SCSI card, so I assume it would cache something that's already
> cached, right?  How do you work around that?  Is there some way of telling

Yes. 

> it "hey, don't be very aggressive with your disk caching"?  Or is it such
> a low priority thing that memory isn't used for cache unless there's no
> other use for it?

I don't think there is a way to 'tell' the kernel there is (non volatile
please) writeback cache on a RAIDbox.

Wilko
_     ______________________________________________________________________
 |   / o / /  _  Bulte 				  email: wilko @ yedi.iaf.nl 
 |/|/ / / /( (_) Arnhem, The Netherlands          WWW:   http://www.tcja.nl
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