From owner-freebsd-fs  Thu Sep 21 13:47:42 2000
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Date: Thu, 21 Sep 2000 13:37:46 -0700 (PDT)
From: Matthew Jacob <mjacob@feral.com>
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To: Terry Lambert <tlambert@primenet.com>
Cc: Marius Bendiksen <mbendiks@eunet.no>,
	Stephen Byan <Stephen.Byan@quantum.com>,
	"'Soren Schmidt'" <sos@freebsd.dk>, fs@FreeBSD.ORG, sos@FreeBSD.ORG,
	freeBSD-scsi@FreeBSD.ORG
Subject: Re: disable write caching with softupdates?
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> Really, the OS needs to know the cache strategy of the drive, and
> follow the same strategy itself, to reduce the number of drive to
> OS transactions, and to remove the problem of the drive having to
> go back to the well for a subsequent read, if the cache contents
> are effectively discarded.


It's simple enough- at least with SCSI. If you enable write cacheing, you
should then allow for the filesystem to issue an ioctl that can use the
SYNCHRONIZE CACHE command to provide the commit point.

There are also flavors of readns and writes that can affect cache
retention policies for certain blocks.








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