Date: Fri, 02 Oct 1998 13:46:43 -0600 From: "Justin T. Gibbs" <gibbs@plutotech.com> To: Julian Elischer <julian@whistle.com> Cc: Don Lewis <Don.Lewis@tsc.tdk.com>, freebsd-fs@FreeBSD.ORG, freebsd-scsi@FreeBSD.ORG Subject: Re: filesystem safety and SCSI disk write caching Message-ID: <199810021953.NAA12817@pluto.plutotech.com> In-Reply-To: Your message of "Fri, 02 Oct 1998 11:59:26 PDT." <Pine.BSF.3.95.981002115603.15828A-100000@current1.whistle.com>
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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, Justin To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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