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Date:      Mon, 8 Jul 2002 19:53:16 -0500 (CDT)
From:      Mike Silbersack <silby@silby.com>
To:        Peter Wemm <peter@wemm.org>
Cc:        Julian Elischer <julian@elischer.org>, John Nielsen <hackers@jnielsen.net>, <hackers@FreeBSD.ORG>
Subject:   Re: offtopic: low level format of IDE drive. 
Message-ID:  <20020708195133.K19349-100000@patrocles.silby.com>
In-Reply-To: <20020708233721.DC2C33808@overcee.wemm.org>

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On Mon, 8 Jul 2002, Peter Wemm wrote:

> The thing is, just about all IDE drives more than a few GB or so do 'track
> writing' and have no fixed sectoring or sector positioning.  ie: each time
> you write a single sector to a track, it does a read-modify-write of *THE
> ENTIRE TRACK*.  This is why we have to have write caching turned on for IDE

> The sad thing is that this makes softdep almost completely useless, because
> the basic assumption is that sectors that were not explicitly written to
> will not be touched.  The problem is that this isn't the case, even with
> write caching turned off.  Writing a single sector causes the drive to
> completely rebuild the track and all the sectors on it... in a different

So, this basically means that even a journalling filesystem wouldn't be
much safer... how about battery backed up controllers - would those
provide protection?  (I suspect not, but maybe they're more sophisticated
than I thought.)

Mike "Silby" Silbersack


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