Return to BSD News archive
Path: euryale.cc.adfa.oz.au!newshost.anu.edu.au!harbinger.cc.monash.edu.au!news.rmit.EDU.AU!news.unimelb.EDU.AU!munnari.OZ.AU!news.mel.connect.com.au!news.syd.connect.com.au!gidora.zeta.org.au!not-for-mail
From: bde@zeta.org.au (Bruce Evans)
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: Fun with slices and partitions
Date: 28 Jul 1996 23:40:23 +1000
Organization: Kralizec Dialup Unix
Lines: 67
Message-ID: <4tfqk7$kfq@godzilla.zeta.org.au>
References: <uybk7b3br.fsf@losira.ppe.bb-data.de>
NNTP-Posting-Host: godzilla.zeta.org.au
In article <uybk7b3br.fsf@losira.ppe.bb-data.de>,
Martin Ibert <mib@bb-data.de> wrote:
>In article <SCOTT.96Jul16124600@crux.dcs.qmw.ac.uk> scott@crux.dcs.qmw.ac.uk (Scott Mitchell) writes:
>
>: Yep, wrong way around. Four _slices_ per disk (what DOS fdisk calls
>: partitions), and a bunch of BSD _partitions_ in each slice (8, IIRC).
>
>*sigh* Yes, strangely enough, FreeBSD choose to pervert the
>well-established name hierarchy of top-level partitions and
>second-level slices and do it the other way around.
How would you do it? You have to support the well-established
4.4BSD name hierarchy of 8 top level partitions and 0 second level
slices. You have to support the well-established 4.4BSD disklabel
format for storing the partition information. This must work on
disks without a 4.4BSD disklabel and on disks with arbitrarily
foreign formats for the partition information. You have to support
nth-level partitions in foreign partition formats (n = 2 occurs in
practice for (DOS) logical drives within (DOS) extended partitions).
>system". Windows NT, OS/2, Linux and of course MS-DOS (which I would
>easily agree is not an operating system) all can use more than one
>fdisk partition (either primary or extended, which means a set of smaller fdisk
>partitions inside a big primary fdisk partition -- to get around the limit
>of 4 primary fdisk partitions per drive) and do not employ any
>OS-specific substructuring -- each fdisk partition becomes a block
>device of its own, for a file system (or swap space, or
>what-have-you).
So can FreeBSD. E.g., to put a file system on /dev/rsd0s5 (the first
"extended" fdisk partition):
newfs -s 12345678 /dev/rsd0s5 dummylabel
Here I had to specify the file system size and a dummy label because there
is no label on the disk.
>support extended ones). Also, integration with other filesystems is a
>lot easier that way; there is a canonical and easily understood way of
>addressing the hard disk areas used by other operating
>systems. Mounting DOS fdisk partitions from Linux is practically
>hassle-free, for example.
No, there is no canonical way of:
(1) naming DOS drives. The names change when you a add a drive in the
middle and when a drive in the middle dies.
(2) numbering primary partitions. Old versions of DOS (3.0?) number
them back to front.
(3) addressing logical drives within extended partitions. Extended
partitions form a quaternary tree. Operating systems should only
create degenerate forms of the tree that are equivalent to linked
lists, but all forms should be accepted and there is only a canonical
traversal order for degenerate forms.
(4) handling huge numbers of partitions. DOS can only handle 26 partitions
(A: - Z:) on all drives. Linux can only handle 11 logical drives
(5-15) per drive. FreeBSD can only handle 26 logical drives
(s5-s30) per drive.
Thus mounting DOS fdisk partitions from Linux is only practically
hassle free in the usual case :-). Mounting DOS fdisk partitions
from FreeSBD is essentially the same:
Linux: mount -t msdos /dev/sda5 /mnt
FreeBSD: cd /dev; sh MAKEDEV sd0s5 # if necessary
mount -t msdosfs /dev/sd0s5 /mnt
--
Bruce Evans bde@zeta.org.au