31 Dec
2023
31 Dec
'23
11:38 p.m.
The different overlapping partitions predates disk labels.
Up to and including 4.3 BSD, to change the size of partitions
on a particular disk, you had to recompile the kernel.
They were that way so that if you had multiple disks, you
could use one for root + swap + some thing small and use another
whole disk for a single filesystem.
It was also helpful, if you had the drives, to nightly dd
your real root to the "a" partition on another, identical
drive, so that you could boot the backup root in an emergency.
I don't remember for sure, but I think that Ultrix may have
been the first BSD-style system to have disk labels, followed
by some version of SunOS. All of that is way in the distant
past though: mid- to late 80's.
I am guessing that the original conventions date back to
V7 or 32V, but one would have to go looking at code to be sure.
HTH,
Arnold
Grant Taylor via TUHS <tuhs(a)tuhs.org> wrote:
Hi,
I've found myself wondering about partitions inside of BSD disk labels.
Specifically, when and where was the convention that "a" is root, "b"
is
swap, etc?
I also understand the "c" partition to be the entire disk, unless it
isn't, at which point it's the entire slice (BIOS / MBR partition)
containing the BSD disklabel and "d" is the entire disk.
I also found something last night that indicated that OpenBSD uses disk
labels somewhat differently than FreeBSD.
Aside: This is one of the dangers of wondering how something curious
came to be and why it came to be when working on 10-15 year old FreeBSD
systems.
--
Grant. . . .