Date: Fri, 2 Oct 1998 22:03:35 +0000 (GMT) From: Terry Lambert <tlambert@primenet.com> To: gibbs@plutotech.com (Justin T. Gibbs) Cc: julian@whistle.com, Don.Lewis@tsc.tdk.com, freebsd-fs@FreeBSD.ORG, freebsd-scsi@FreeBSD.ORG Subject: Re: filesystem safety and SCSI disk write caching Message-ID: <199810022203.PAA21941@usr08.primenet.com> In-Reply-To: <199810021953.NAA12817@pluto.plutotech.com> from "Justin T. Gibbs" at Oct 2, 98 01:46:43 pm
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> >write caching can screw soft updates if there is any > >major re-ordering of the data written. > > Only if you lose power or have a buggy device. Go read the SCSI spec on > write caching. > > >With tags it doesn't matter if they are re-ordered, as long > >as they are not acknowledged until they are on the platter. > > 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. Re-ordered writes are allowed, but, only > such that it maintains read/write coherency. This is with the restrictive > ordering semantics that drives usually ship with by default. You can turn > on "re-order at will" through a mode page. > > Waiting for Terry's long winded response to this thread, I told you so. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message
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