From owner-freebsd-fs  Thu Sep 21  8:16: 4 2000
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Message-ID: <8133266FE373D11190CD00805FA768BF055BD1D7@shrcmsg1.tdh.qntm.com>
From: Stephen Byan <Stephen.Byan@quantum.com>
To: "'Justin Gibbs'" <gibbs@plutotech.com>,
	Stephen Byan <Stephen.Byan@quantum.com>
Cc: mbendiks@eunet.no, Stephen Byan <Stephen.Byan@quantum.com>,
	fs@FreeBSD.ORG, sos@FreeBSD.ORG, freeBSD-scsi@FreeBSD.ORG
Subject: RE: disable write caching with softupdates?
Date: Thu, 21 Sep 2000 08:15:50 -0700
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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.
 
Regards,
-Steve


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