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	Sat, 14 Mar 1998 15:37:00 +1100
Date: Sat, 14 Mar 1998 15:37:00 +1100
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199803140437.PAA19697@godzilla.zeta.org.au>
To: mike@smith.net.au, obrien@NUXI.com
Subject: Re: *HEADS UP* Correction to previous postings.
Cc: current@FreeBSD.ORG, joerg@FreeBSD.ORG, stable@FreeBSD.ORG
Sender: owner-freebsd-stable@FreeBSD.ORG
Precedence: bulk

>In light of the new mount changes, how should these instructions from
>Jo"rg be updated?
>
>    dd if=/dev/zero of=/dev/rsd2 bs=1k count=1
>    disklabel -Brw sd2 auto
>    disklabel -e sd2
>    newfs -d0 /dev/rsd2e
>    fsck /dev/sd2e

No change.

>Is the slice created by ``disklable .. auto'' always "s1"?

It depends.  If you have cleared the DOS partition table using dd as
above, then `disklabel ... auto' gives a bogus partition entry in the
slot normally occupied by slice s4.  The kernel initially reports
this as slice s5, but the driver won't create any slices, and the
kernel will later mount sd2e (if you booted from that instead of the
default sd2a, and nothing else goes wrong).

>Doesn't a dedicatedly partitioned disk, really not contain slices?

Depends how it was dedicated.  There are several cases:
1. as above.
2. as above, then run fdisk to change the 4th partition entry in
   any way (e.g., to de-bogotify or clear it).  Then you really get
   real slices (probably broken ones if the 4th entry is changed
   to anything except an entry covering the whole disk).
3. as in (2), but prepare the 4th entry before running disklabel,
   and skip the dd step.
4. as in (1), but leave out -B.  Then you get an all-zero MBR,
   really without real slices.  Disks configured in this way can't
   be booted from directly.
5. as in (1), but edit the MBR to remove the 0xAA55 signature.
   Then you get an ignored MBR, effectively without real slices.
   It may be possible to boot from disk configured in this way
   (depends on the BIOS).

>fdisk(8) reports them as living in [fdisk] partition 4.  Can't tell what
>sysinstall would do in "dangerous dedicated mode" as it won't see the
>drives on my second SCSI bus. :(

Sysinstall doesn't seem to provide d.d. mode by default.  The default
for "A Use Entire Disk" seems to be to not actually use the entire
disk, but to use real slices and the entire disk except for the MBR
(and other sectors on the first "track"?).

>    fsck /dev/sd2s1e 
>    Can't open /dev/rsd2s1e: Device not configured
>    fsck /dev/sd2s4e 
>    Can't open /dev/rsd2s4e: Device not configured
>
>    dd if=/dev/zero of=/dev/rsd2 bs=1k count=1
>    disklabel -Brw sd2s1 auto
>    disklabel: /dev/rsd2s1e: Device not configured
>    disklabel -Brw sd2s4 auto
>    disklabel: /dev/rsd2s4e: Device not configured
>
>So what's the new way?

Same as before: don't use slices when you don't have them.

Bruce

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