Date: Thu, 4 Oct 2001 18:08:57 -0400 (EDT) From: Zhihui Zhang <zzhang@cs.binghamton.edu> To: Mike Meyer <mwm@mired.org> Cc: Magdalinin Kirill <bsdforumen@hotmail.com>, questions@FreeBSD.ORG Subject: Re: turning off write cache on SCSI drive Message-ID: <Pine.SOL.4.21.0110041759390.13175-100000@onyx> In-Reply-To: <15292.51953.728016.474117@guru.mired.org>
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On Thu, 4 Oct 2001, Mike Meyer wrote: > Zhihui Zhang <zzhang@cs.binghamton.edu> types: > > On Thu, 4 Oct 2001, Mike Meyer wrote: > > > > > Magdalinin Kirill <bsdforumen@hotmail.com> types: > > > > Hello, > > > > some mail posts on softupdates says that turning off write cache is > > > > prerequisite for it. > > > They're generally talking about IDE drives. SCSI drives have tagged > > > queuing, which means you're perfectly safe doing this. > > Why tagged queuing make it safe to turn WCE on? > > The problem that WCE presents is that a write to the drive returns, > but the data isn't really on the drive. Tagged queuing allows the > drive to tell the software when the data is really on the drive. Can you be more specific on this? I searched the mailing list archive, one posting says: Tagged transactions may "complete" in a non-FIFO order. "Complete" either means data transfered into the cache or data safely on the media depending on whether the cache is enabled. Thanks, -Zhihui To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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