Had the following conversation elsewhere. I put comment characters in front of my anonymous correspondent's comments.
> Also [an available firewire drive]
> is set up with a DOS type partition map and two ext3 partitions, you
> could temporarily reformat one as HFS+ or VFAT if you needed to, *but*
> I don't know if MacOS will do this if it is a DOS rather than Apple
> type partition map ...
> As far as I know, you can't boot linux on PPC when its installed on an
> external firewire drive - you probably knew that but I thought I
> should mention it.
Yes, I encountered that worry late last night (after sending you the message),
although I am still not entirely convinced of its truth. People say that you can
set the bootup disk in the mac osx settings to an external hdd, or use the keys
to select a disk.
It should hence be possible to put the linux boot loader on the external, and
just boot that. I have not been able to verify whether any of these cheats work
on a PowerMac G3, however. Your drive would come in handy at that moment - at
least if the architecture allows booting from the drive, it ought to show up in
the list given after pressing the above keys at startup. On the other hand,
linux may not be a compatible OS for this procedure.
> I have a strong suspicion that you will not be able to check this
> using my drive because open firmware can only see Apple partition
> maps, and HFS, HFS+ and (maybe on later versions) UFS file systems.
> The reason I suspect this is that when Linux on a PPC is installed on
> an *internal* drive it has to have an Apple partition map and the boot
> loader has to go in a HFS partition (because write access to HFS+ and
> UFS is experimental under Linux 2.4 kernels). [...] However, from what you say it seems as > though it would be
> possible in principle if one had a firewire drive with an Apple
> partition map, or a blank one ...
> But, installing on an external FW drive is going to involve a slightly
> gnarly nonautomatic installation process, even if the subsequent
> alternate booting works in a straightforward way.
> I think that if I were in your position I would:
> 1. Buy a [big] FW drive , format [part of] it as
> HFS/HFS+ and copy everything off your machine onto it. I find
> having a mirror (or even the primary copy) of all my work files on
> a portable disk to be a very handy way of working.
> 2. Scrub the hard disk on your machine.
> 3. Do a clean OSX and Linux install on your machine and migrate
> essential stuff back, see how much space is left.
> 4. If neccessary keep some stuff on the FW drive (perhaps reformatted
> with one HFS+ and one or more linux partitions). You would not have
> to do anything too gnarly if you had the bootloader and root Linux
> partitions on your internal disk, and put /usr and /home (say) on
> the external drive.