Date: Thu, 21 Sep 2000 17:26:17 +0200 (CEST)
From: Soren Schmidt <sos@freebsd.dk>
To: Stephen.Byan@quantum.com (Stephen Byan)
Cc: gibbs@plutotech.com ('Justin Gibbs'), mbendiks@eunet.no, fs@FreeBSD.ORG, sos@FreeBSD.ORG, freeBSD-scsi@FreeBSD.ORG
Subject: Re: disable write caching with softupdates?
Message-ID: <200009211526.RAA98589@freebsd.dk>
In-Reply-To: <8133266FE373D11190CD00805FA768BF055BD1D7@shrcmsg1.tdh.qntm.com> from Stephen Byan at "Sep 21, 2000 08:15:50 am"
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It seems Stephen Byan wrote: > Justin Gibbs [mailto:gibbs@plutotech.com] wrote: > > > > Without write caching, you pay one disk rotation for each > > sequential write. > > > > This should not be the case if you are allowed to overlap > > commands. The > > only penalty should be increased latency in seeing a write complete. > > You're correct. I was writing with respect to ATA drives, of which I believe > only IBM's support write queuing, so I overlooked the case where queuing is > available. > > I'm not that familiar with ATA in practice; the spec for ATA queuing looked > sufficiently convoluted (i.e. a kludge) that it wasn't obvious to me that it > would be a performance win to implement it. Well, but it is, I see 5-10% performance gain using tagged queing, so its definitively worth the trouble. I dont think it is that bad, it was easy enough to implement support for in the ATA driver, but so fa I think we are alone in actually using it :) -Søren To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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