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Date: Thu, 6 Apr 1995 23:45:33 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199504061345.XAA21963@godzilla.zeta.org.au>
To: rgrimes@gndrsh.aac.dev.com, roberto@blaise.ibp.fr
Subject: Re: Label/slices : how to add a disk ?
Cc: bde@zeta.org.au, freebsd-current@FreeBSD.org
Sender: current-owner@FreeBSD.org
Precedence: bulk

>> I just got a brand new disk, Conner CFP1080S, geometry reported by boot -v
>> is (3659/6/96). The standard translation would give me 1030/64/32.
>>
>> I've been unable to even put a label on it :-(
>> ...
>> Apr  6 02:44:26 keltia /kernel: (bt0:2:0): "CONNER CFP1080S 3939" is a type 0 fixed SCSI 2
>> Apr  6 02:44:26 keltia /kernel: sd2(bt0:2:0): Direct-Access 1030MB (2110812 512 byte sectors)
>> ...
>> fdisk /dev/sd2
>> ******* Working on device /dev/sd2 *******
>> parameters extracted from in-core disklabel are:
>> cylinders=3658 heads=64 sectors/track=32 (2048 blks/cyl)
>>           ^^^^      ^^^^             ^^^
>>           good      wrong            wrong

Actually:-)  wrong     good             good

>Nope, use the override what the BIOS thinks and tell it
>cyliders=1030, heads=64, sectors/track=32.

The dummy in-core label for /dev/sd2 is supposed to give the BIOS
geometry, but it got the number of cylinders wrong (known bug, it
doesn't change it from the H=6/S=96 geometry to the H=64/S=32.  There
are a lot of different numbers for the number of cylinders for the 6/96
geometry!  The BIOS says 3659, the dummy label says 3658, but
2110812/8/96 is 3664 with a remainder of 348.  1030/64/32 is correct
(remainder 1372).

>> The data for partition 3 is:
>> sysid 165,(FreeBSD/NetBSD/386BSD)
>>     start 0, size 2097152 (1024 Meg), flag 80
>> 	beg: cyl 0/ sector 0/ head 0;
>                    ^^^^^^^^^

>Redo the fdisk -u, override the calculation of beg/end.  Use
>cyl 0, sect 1, head 0 for the beg.  The default caclulations screw
>up and put 0 in for the starting sector :-(.

Another known bug.  I didn't expect it to cause so much trouble.  I
expected people who use the whole disk for FreeBSD to not even run
fdisk.

For this to work, you have to have a disk that doesn't have a partition
table.  This is easy to arrange by overwriting the partition table:
	dd if=/dev/zero of=/dev/rsd2 count=1
to clear the MBR or
	dd if=/dev/zero of=/dev/sd2 bs=1 seek=46 count=66
to clear the partition table (leaving the bootstrap intact) or
	dd if=/dev/zero of=/dev/sd2 bs=1 seek=510 count=2
to clear only the partition-table-valid magic.

Then normal (poor) BSD methods apply:
	disklabel -w -r [-B] sd2 disktabentry [...]
The driver knows almost everything about the disk geometry and puts it
in the dummy in-core label on for /dev/rsd2, but there is no convenient
way to get the geometry onto the disk /dev/rsd2c.  There is no dummy
in-core label for /dev/rsd2c because the disk isn't considered to be
a BSD disk until it is labeled.

Bruce