Date: Sat, 6 Dec 2003 16:44:36 -0800 (PST) From: Nate Lawson <nate@root.org> To: Don Lewis <truckman@FreeBSD.org> Cc: freebsd-scsi@FreeBSD.org Subject: Re: More Adaptec 29320 + Seagate ST336607LW woes Message-ID: <20031206164352.K33312@root.org> In-Reply-To: <200312061929.hB6JTpeF042644@gw.catspoiler.org> References: <200312061929.hB6JTpeF042644@gw.catspoiler.org>
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On Sat, 6 Dec 2003, Don Lewis wrote: > On 6 Dec, ian j hart wrote: > > I thought tagged queuing needed WCE. > > One place where folks have noticed a performance difference between WCE > on and WCE off is when using newfs after we got rid of the buffered > block devices and forced newfs to use the raw character device. Newfs > only issues one write() at a time and waits for the status before > issuing another write(). If WCE is on, the writes only have to hit the > drive cache before the drive returns a status that gets returned to > userland, but if WCE is off the data has to hit the platter before the > status is returned, which slows down newfs quite considerably. Tagged > queuing doesn't make any difference in this case because the drive will > only see at most only one command at a time. Great explanation. We should probably add write clustering to newfs at some point. -Nate
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