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Date: Wed, 14 Oct 1998 19:50:59 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199810140950.TAA17421@godzilla.zeta.org.au>
To: bde@zeta.org.au, sos@FreeBSD.ORG
Subject: Re: bitten 3 times already.
Cc: freebsd-current@FreeBSD.ORG, Marius.Bendiksen@scancall.no
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>> The geometry or geometries used by previously active driver(s) are almost
>> irrelevant, as you should know if you have written an IDE driver :-).
>> The only thing that's important (for the driver) to know is that the
>> drive actually uses the geometry that the driver programs it to use.
>
>Erhm, and where is the difference ? :)

Everywhere.  The driver gets to choose the geometry.  There is no need for
it to match previous choices; the choice just needs to be acceptable to
the drive, and have enough sectors and heads for all physical sectors to
be addressable.  The FreeBSD driver chooses to use the default geometry
because this is most likely to satisfy both constraints.  On drives
larger than 504MB, the default geometry is very _un_likely to match
previous choices (except choices by the same driver, of course).

>It not so important that the geometry matches the drive, as its important
>that its the same geometry that was used when the data was written..

No, the current geometry is very important, but the geometry used to write
the data is unimportant.  The driver may changes the geometry between
transactions.  This would be silly, but old versions of the FreeBSD driver
actually changed the geometry 2 or 3 times during first-opens.

Bruce

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