Date: Wed, 12 Apr 2000 16:25:04 +0930 From: Greg Lehey <grog@lemis.com> To: `ekips <ekips@whack.org> Cc: freebsd-questions@FreeBSD.ORG, freebsd-newbies.com@whack.org Subject: Re: "dangerously dedicated" Message-ID: <20000412162504.N35391@freebie.lemis.com> In-Reply-To: <Pine.GSO.4.21.0004112110230.16167-100000@apogee.whack.org> References: <Pine.GSO.4.21.0004112110230.16167-100000@apogee.whack.org>
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[trimming -newbies; this is a question]
On Tuesday, 11 April 2000 at 21:37:54 -0700, `ekips wrote:
> when making partitions with /stand/sysinstall, i decided to press "A" and
> got the following message:
>
> "Do you want to do this with a true partition entry so as to remain
> cooperative with any future operating systemss on the drive(s)?"
>
> ... and then points me to the FreeBSD FAQ, where i could not find any info
> on the subject. where can i find good documentation on this? or even
> better, could someone explain all the ramifications of my two options
> [yes/no].
There is some disagreement amongst FreeBSD developers as to how
"dangerous" dedication really is. Here's a brief version:
1. Under UNIX, we used a partitioning scheme which expected disks to
be used by one operating system only. In BSD UNIX, we had a
partition table with up to 8 entries. UNIX System V used a
different layout with up to 16 entries, some of which had very
specialized usages. Either way, this partition table was the key
to the entire disk.
2. On the PC, Microsoft developed its own partitioning, with a
maximum of four partitions. This number soon proved to be too
little, so they added things called extended partitions, which
were really partitions within partitions.
3. When we started porting UNIX to the PC, we kept the original BSD
or System V layout and put it in one Microsoft partition, rather
like an extended partition. This enabled the system to run up to
four different operating systems, each from a different Microsoft
partition.
Enjoying the double use of the word "partition"? We don't. As a
result, we call the Microsoft partitions "slices", and continue to
call the UNIX partitions "partitions".
4. If you only want to run one operating system ("dedicated" mode),
there's no obvious reason to use a Microsoft partition table.
Instead, you could just write the UNIX partition table at the
beginning of the disk, like we did in the old days (point 1
above). But you could also have a Microsoft partition table with
only one entry. The Microsoft partition table can waste up to 200
or 300 kB of disk space, and has no obvious advantage.
5. Unfortunately, most BIOS manufacturers build their BIOS to run
Microsoft. Some expect to find a Microsoft partition table in
sector 0 of the disk. If they don't find it, they can't figure
out the geometry of the drive, and effectively the drive becomes
inaccessible until after you have booted (FreeBSD has no
trouble). If this is not the system disk, there's no problem, but
you need to boot from the system disk, so this effectively blows
you out of the water. This is "dangerous".
Getting back to your question: the question refers to the type of
dedication. The "true" partition entry is really a slice, or
Microsoft partition entry, which implies a Microsoft partition table.
If you have a Microsoft partition table, you don't have a problem, but
you can also lose some data. If you don't have a Microsoft partition
table, and if your BIOS is broken, you may find that you can't boot.
The danger is limited to the possibilty that you might have to
reinstall if it doesn't boot the first time round.
I've seen a couple of cases where it looked as if I had a broken BIOS
machine, but it always turned out to be some other problem. I
personally use only "dangerously dedicated" disks, since I have no use
for Microsoft.
Greg
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