Re: Want to move from root LVM/LILO to LVM/Grub
On Mon, Oct 03, 2005 at 01:06:16PM -0500, Jason Martens wrote:
> >>>I believe your /boot partition needs to be on a non LVM partition.
> >>Well, I can boot just fine with a root partition on the LVM volume using
> >>LILO. I believe this is because my initrd has the LVM drivers included,
> >>so it can recognize the root partition.
> >he said /boot, not 'root'.
> Ah, so he did. However, as I said earlier, I can boot even though I
> have no /boot partition, and root is in LVM.
There is a difference between lilo and grub in how they find the disk
sectors containing the kernel image and the initial ram disk.
Lilo determines the sector numbers while linux is running (before the
reboot), when you issue the command "lilo". It stores these numbers in a
map file, the sector numbers of which are in turn determined and stored
in a reserved region of the lilo boot sector.
On bootup, lilo simply loads the predetermined sectors - first the map
file, then the kernel image and optionally an initial ram disk.
This way, lilo does not need any special support for LVM, it can just
make use of the underlying OS drivers to find the sectors.
Grub tries to find the sectors containing the kernel image during the
boot process. To that end, it has a built-in driver for the root
partition's filesystem. When installing grub as boot loader, a suitable
variant of grub with the correct filesystem driver was chosen (this
explanation is somewhat simplified). In order to load a kernel image
from a filesystem stored on an LVM volume, grub would need to support
LVM read access in addition to the filesystem.
I didn't verify it, but I suspect there is no grub version with such
support.
Regards,
Mirko
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