Date: Wed, 15 Jan 2003 10:38:44 -0600 From: Mike Meyer <mwm-dated-1043080725.8426fd@mired.org> To: swear@attbi.com (Gary W. Swearingen) Cc: Ian Dowse <iedowse@maths.tcd.ie>, freebsd-questions@freebsd.org Subject: Re: Dangerously dedicated vs. fully dedicated, etc. Message-ID: <15909.36500.590269.54350@guru.mired.org> In-Reply-To: <h7k7h7uy17.7h7@localhost.localdomain> References: <200301141936.aa93359@salmon.maths.tcd.ie> <h7k7h7uy17.7h7@localhost.localdomain>
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In <h7k7h7uy17.7h7@localhost.localdomain>, Gary W. Swearingen <swear@attbi.com> typed:
> Ian Dowse <iedowse@maths.tcd.ie> writes:
> You've cleared up several things, thanks. (I still don't see why any
> BIOS would have trouble with a DD disk, leading to DD's deprecation, but
> I can just take people's word for it, for the task at hand.) BTW, I've
> seen both of your options referred to as DD, if I understood it right.
There are BIOSes out there that check sector 0, and fail to recognize
the disk if it if the MBR doesn't conform to their idea of
"valid". Some of them will overwite sector 0 with a "valid" MBR in
that case. I've had this happen to me, meaning my disk was fried every
time I rebooted the system - until I turned off the "Virus protection"
feature of the BIOS.
> > (C) Dedicated format using dummy slice
> ...
> One such as would be created by "disklabel -B". (/boot/boot1 seems to
> have the fourth slice pre-defined.) This differs from "B" only in the
> slice table, right? The "disklabel" manpage implies that this is a DD.
Yes, the slice table is the only difference. This is what you get if
you install a "dangerously dedicated" disk with the i386 installer. In
fact, I've got one here:
Information from DOS bootblock is:
The data for partition 1 is:
sysid 165,(FreeBSD/NetBSD/386BSD)
start 0, size 17942584 (8761 Meg), flag 80 (active)
beg: cyl 0/ head 0/ sector 1;
end: cyl 1023/ head 17/ sector 4
The data for partition 2 is:
<UNUSED>
The data for partition 3 is:
<UNUSED>
The data for partition 4 is:
<UNUSED>
> It seems that a DD disk is one which is similar to a single slice
> starting at sector 0, regardless of what the slice table part of sector
> 0 contains. With FreeBSD-standard boot code and some BIOSes, one disk
> layout (ie, DD or sliced) will work better than the other. (And for DD
> disks, some slice table contents might work better than others. I've
> not read anything comparing your "B" and "C" or either with a slice
> table full of zeros or random bits.)
As you can see, it's sector 1, not sector 0. Everything else seems to
be correct.
<mike
--
Mike Meyer <mwm@mired.org> http://www.mired.org/consulting.html
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.
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