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Date:      Sat, 12 Jan 2002 05:02:47 -0600
From:      "Mike Meyer" <mwm-dated-1011265367.36e001@mired.org>
To:        Bjarne Wichmann Petersen <freebsd.nospam@mekanix.dk>, swear@blarg.net (Gary W. Swearingen)
Cc:        questions@freebsd.org
Subject:   Re: Limitations of BSD-slices.
Message-ID:  <15424.6103.544570.250164@guru.mired.org>
In-Reply-To: <78852280@toto.iv>

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Gary W. Swearingen <swear@blarg.net> types:
> Bjarne Wichmann Petersen <freebsd.nospam@mekanix.dk> writes:
> > I've found that FreeBSD is still "hogging" a primary partition/slice

No, you've found that the default install is doing that. FreeBSD
certainly understands extended slices, and you can put BSD partitions
in them with no problem. So clearly you can put a FreeBSD system in an
extended slice. Getting it to boot is a more interesting problem.

> > and I've only got 4 partition within a slice, a-d being reserved and h
> > being the maximum.

Again, you're describing the default installation, not real
limits. The only partitions that are reserved are a and c. If you're
going to boot a partition, it has to be a. It may have to start at
offset zero to boot as well, but I haven't tried changing that
one. Various things get upset if c isn't the whole disk, but you're
free to use it it for data if you want to. There are no restriction on
b and d.  In other words, you actually get 7 partitions in a slice to
use, with the caveat that you have to boot from a.

> > Why is it limited to h?
> I'll guess that there's a 8-bit field somewhere that would be awkward to
> "fix".

Why guess when the source is available? It's a three-bit field, and
it's part of the device number used for references to disk
devices. All the changes *should* be encapsulated in disklabel.h. The
changes are both obvious and straightforward. There's a reference to
reboot.h there, which has an 8-bit field for partitions, so you'd have
to fix that if you wanted more than 256 partitions.

I have no idea whether the resulting system would work properly or
not. You certainly couldn't install that kernel and then boot
multiuser on a system that was installed with the old value in
place. I'd be surprised if it you could get to a single-user prompt.

All of which is irrelevant to the question of "why is it limited to
h?". The answer to that one is "Because 8 is enough."

	<mike
--
Mike Meyer <mwm@mired.org>			http://www.mired.org/home/mwm/
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.

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