Date: Wed, 17 Oct 2001 14:03:18 -0400 (EDT) From: carter@pair.com To: freebsd-hardware@FreeBSD.ORG Subject: Re: soft updates, write cache Message-ID: <20011017180318.66984.qmail@smx.pair.com> In-Reply-To: <20011017104044.Y5727-100000@bronze.greatschools.net> from John David Duncan at "Oct 17, 1 10:53:53 am"
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> > On Wed, 17 Oct 2001 carter@pair.com wrote: > > > Hello, > > > > I'm a bit unclear on the interactions of soft-updates and drive write cache. > > I hear one should disable the write cache on IDE/ATA drives when using > > soft-updates. > > Why? > > This is the second reference I've seen to this on this list, but there is > no mention of it at www.mckusick.com or in the softupdates code... and > there's not any immediately intuitive problem, either; scsi adapters and > drives have long performed many levels of caching. > > - JD From what I understand, softupdates allows the filesystem to always be in a 'clean' state, so that fsck is not necessary after a crash except to reclaim free space from deleted files. If softupdates depends on the files having actually been written, their being stored in a hardware write cache can lead to the OS believing a filesystem is clean when it is not. As well, I have seen reference to IDE devices lieing about if their cache has been written or not. That's the best I can guess on it, at any rate. Chris Carter To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hardware" in the body of the message
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