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Date:      Tue, 9 Jul 2002 13:08:02 +1000
From:      "Chris Knight" <chris@aims.com.au>
To:        <peter@wemm.org>
Cc:        <silby@silby.com>, <hackers@FreeBSD.ORG>
Subject:   RE: offtopic: low level format of IDE drive.
Message-ID:  <004701c226f5$d7a0d540$020aa8c0@aims.private>
In-Reply-To: <20020709024345.8095A3808@overcee.wemm.org>

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Howdy,

> -----Original Message-----
> From: owner-freebsd-hackers@FreeBSD.ORG
> [mailto:owner-freebsd-hackers@FreeBSD.ORG]On Behalf Of Peter Wemm
> Sent: Tuesday, 9 July 2002 12:44
> To: chris@aims.com.au
> Cc: silby@silby.com; hackers@FreeBSD.ORG
> Subject: Re: offtopic: low level format of IDE drive.
> 
> [snip]
> > Does anyone have a detailed list of which SCSI drives do 
> > track writes rather than sector writes?
> 
> You can find out by turning write caching on and off.  
> camcontrol modepage daN.  You want -m 8, the WCE bit. (write cache
> enable).  I do not remember which -P args you need.
> 
> If you see a HUGE difference in writing smallish blocks to disk
> between WCE on vs off, then you have a track write drive.
> 
> A true sectored drive would have much less of a slowdown.  I do
> not have a comparable set handy to get a better idea of what to
> expect.  
> Really small writes cost scsi overhead though, so that adds to
> the slowdown.  If I was to take a best guiess, I would expect a
> factor 10+ slowdown for track-write drives on 4K blocksize writes,
> vs factor 2-5 slowdown for a sectored drive.
> This is the slowdown factor when turning WCE off.
> 
Excellent. This information should prove invaluable for future drive
testing and acceptance. Thanks.

> Cheers,
> -Peter

Regards,
Chris Knight
Systems Administrator
AIMS Independent Computer Professionals
Tel: +61 3 6334 6664  Fax: +61 3 6331 7032  Mob: +61 419 528 795
Web: http://www.aims.com.au 


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