Date: Tue, 29 Oct 2002 17:28:24 -0800 From: Peter Wemm <peter@wemm.org> To: Daniel O'Connor <doconnor@gsoft.com.au>, Chuck Robey <chuckr@chuckr.org>, Kenneth Culver <culverk@yumyumyum.org>, "Wilkinson, Alex" <Alex.Wilkinson@dsto.defence.gov.au>, hackers@FreeBSD.ORG Subject: Re: [hardware] Tagged Command Queuing or Larger Cache ? Message-ID: <20021030012824.8E54B2A88D@canning.wemm.org> In-Reply-To: <20021029103133.GA18812@HAL9000.homeunix.com>
next in thread | previous in thread | raw e-mail | index | archive | help
David Schultz wrote:
> Thus spake Peter Wemm <peter@wemm.org>:
> > Actually, not even then. Modern IDE drives only write entire tracks at a
> > time. If you modify a single sector, then the drive has to read the entire
> > track into the buffer, in-place edit the sector, and then rewrite the entir
e
> > track.
> [...]
> > And that completely blows FFS's assumptions out of the water. And what
> > is sad is that many SCSI disks are similar these days. But not all of
> > them (I'm told).
>
> I've heard this before. It would be very useful to have
> information about which drives have this misfeature, but I guess
> it isn't the sort of thing that hard drive manufacturers like to
> advertise. Does anyone have any data on track-writing drives?
IBM used to claim it as a feature and have patents on it. As best as I can
tell, all IDE disks have it since about 1999 or so. Quantum and IBM
certainly did, as it was a way of getting the drive capacity up and
reducing the cost. One way that you can tell is by seeing how big the
slowdown is when write caching is turned off and whether you see the same
slowdown slowdown regardless of any sector interleaving.
ie: if writing to every 10th or 20th (or whatever) sector is just as slow
as writing to every sector with write caching turned off, then you have a
track-write drive. This is because every single sector write causes the
entire track to be written.
Cheers,
-Peter
--
Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com
"All of this is for nothing if we don't go to the stars" - JMS/B5
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-hackers" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20021030012824.8E54B2A88D>