disk partitioning for multiOS machine

[Richard W.M. Jones]

On Mon, Aug 18, 2008 at 05:52:33PM +0300, Ahmed Kamal wrote:
> Sorry this might be a bit off topic. I am getting a new laptop, and plan to
> use fedora as my main OS. I will be installing Windows too for the
> occasional game. I would also like to install open-solaris and/or MacOSX,
> just to see what others are up to. Eventually I will also want to run
> multiple VMs. It would be necessary to share data across those OSs and VMs.
> I am lost as to how to partition/lvm the 250GB drive for optimal use. Does
> anyone have a similar setup? any advice ?

This is how I arranged a similar machine where I wanted to multi-boot
into Windows and several other OSes:

  /dev/sda1   Windows
  /dev/sda2   Shared /boot partition (give it 1 or 2 GB)
  /dev/sda3   LVM PV & single volume group /dev/VolGroup
         within /dev/VolGroup:
           /dev/VolGroup/F10        For Fedora 10/Rawhide
           /dev/VolGroup/F9         For Fedora 9
           /dev/VolGroup/F8         For Fedora 8
           /dev/VolGroup/Debian     For Debian
           /dev/VolGroup/Shared     Shared space (mounted on all OSes)
           /dev/VolGroup/Swap       Shared swap (used by all OSes)

The reasoning behind this was that Windows needs its own primary
partition.  /boot also needs to be on a primary partition because of a
well-known limitation with GRUB.  Everything else was going to run
under Linux so I just have separate LV for each operating system's
root.  Then /dev/VolGroup/Shared is mounted as /mnt/shared on each OS
so I have a space to share data.  I have separate /home directories,
but conceivably you could share these between OSes.

/boot is shared.  When you install a new OS it will "helpfully" trash
the GRUB configuration in /boot/grub/grub.conf, so before you install,
take a copy, then afterwards restore the copy and add a new boot
section for the new OS.  However new OS installs should leave the rest
of /boot untouched *provided* you don't tell them it's OK for them to
format the /boot partition (don't do that!)

Remember that OpenSolaris won't know what to do with LVM.  It will
need a primary partition, unless you're going to run it only
virtualized under a Linux host, in which case you can use LVM for its
virtual disks.  Primary partitions are a pain because changing the
size or rearranging them is next to impossible.  LVM is far more
flexible.

No idea about Mac OS X.  I assume you'd be running the hacked version
of OS X (if your hardware isn't a Mac).

> Would KVM on F10 allow running the non-virtualized (i.e. on disk installed)
> Windows and Solaris to run in full virt mode ?

Yes.  With the configuration above you have a lot of flexibility - you
can both multi-boot and run OSes virtualized from the same LVs.
However you will need to hack /etc/fstab, because disk names will
appear different when running on baremetal versus virtualized.  Also
you can't share /dev/VolGroup/Swap between running OSes (!)

I wouldn't recommend running Windows virtualized under KVM.  There's
lots of random breakage, and even if you do get it working, it'll be
really slow.

Rich.

-- 
Richard Jones, Emerging Technologies, Red Hat  http://et.redhat.com/~rjones
virt-top is 'top' for virtual machines.  Tiny program with many
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