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Date:      Sun, 19 Nov 2000 17:36:21 -0700
From:      Warner Losh <imp@village.org>
To:        Greg Lehey <grog@lemis.com>
Cc:        Sam Zamarripa <samz@oz.net>, stable@FreeBSD.ORG
Subject:   Re: Dedicated disks (was: Dangerously Dedicated) 
Message-ID:  <200011200036.RAA16154@harmony.village.org>
In-Reply-To: Your message of "Mon, 20 Nov 2000 10:52:11 %2B1030." <20001120105211.O58333@echunga.lemis.com> 
References:  <20001120105211.O58333@echunga.lemis.com>  <20001120095100.G58333@echunga.lemis.com> <200011192231.eAJMVIF09854@mass.osd.bsdi.com> <008901c05278$b71a6f50$0200000a@sam> <20001120095100.G58333@echunga.lemis.com> <200011200019.RAA16004@harmony.village.org> 

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In message <20001120105211.O58333@echunga.lemis.com> Greg Lehey writes:
: > No it isn't bogus.  You can't boot off a DD disk on some machines
: > because the MBR is too bogus for the BIOS to cope with.
: 
: So you put a Microsoft partition table on the boot disk.  That doesn't
: mean you need it on the other disks.

On some systems, this works.  On others it doesn't.  Some systems
throw a rod when they see the bogus partition table, even if it isn't
on the primary disk.

: > The problem with DD is that we put a bogus MBR onto the disk.  All
: > that is necessary to fix it would be to put a non-bgous MBR onto the
: > disk.
: 
: Right, for those cases where it's needed.  More specifically, we need
: to now how non-bogus it needs to be.

It must describe most/all of the disk.  It must allow the BIOS to
figure out the geometry so that the boot loader could read the disk
(note, I say could because it might not be the primary disk, and a
bogus partition could cause the BIOS to lose its brain).

I think, and I haven't checked this out yet, that we could make the
partition end c/h/s rounded to the end of the cylinder nearest the
real end of the disk.

Warner



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