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Re: initrd, lvm, and devfs

Alex Owen <rao3@leicester.ac.uk> writes:

> Some of us have woody running on LVM1... well I have this with 2.4 Debian
> kernel and LVM1. For LVM1 to work with a kernel that has devfs compiled in
> (debian kernels for woody do) then /dev/ has to be a mounted devfs.
> For people such as myself sarge as it stands will provide a 2.4.27 kernel
> with devfs and LVM1... This will allow us to upgrade to sarge fairy
> painlessly.
> Debian-installer on the other hand will install sarge on LVM2 and that
> gives people in my position the hint that we need to migrate to LVM2 during
> the lifetime of sarge (and probably 2.6 kernels too).

Debian kernels (2.4.x) are already patched with the device mapper
patches and are fully lvm2 capable. Since lvm2 understands lvm1
metadata you can just update to lvm2 userspace tools, create a new
initrd and reboot.

> During the testing of etch (ie when etch is "testing") debian will hit
> this "removal of devfs" problem... this will not affect sarge (Assuming sarge
> _IS_ released by then). etch is the place to fix the problem. The fix will
> be in 4 parts...
> (1) the kernel package will have no devfs!
> (2) initrd-tools will be fixed to support the kernel packages.
> (3) udev can provide compatability links for devfs names if needed.
> (4) debian-installer will be ported to use udev rather than devfs

Without devfs the syntax of e.g. /proc/partitions changes and anything
parsing those files needs to adapt back to the old syntax.

> People who wish to use non-debian stable kernels on sarge (when it is
> released) will have to backport these fixes from etch to sarge... much as
> I have had to from sarge to woody to get LVM1 to work on woody!
> Taking these in reverse...
> (4) from what I've seen of the d-i work the d-i folks know that a port
> from devfs to udev is on the post sarge todo list.
> (3) udev can alredy provide devfs style device nodes... can it do
> compatability links?
> (2) this thread has alerted initrd-tools people... I hope!
> (1) this thread has alerted kernel people... I hope!
> The only remaining question is are the devfs device names burned into the
> LVM2 metadata stored on disk somewhere??? I suspect not... I think that
> LVM2 uses somekind of UUID to identify devices that form part of an LVM2
> VG. If this UUID business is the case then do we need (3) ???

I've used lvm2 with and without devfs and switched between them
without problems. It's just a matter of changing fstabd and the likes.

> Hopefully by the time etch arrives as stable there will be a sane upgrade
> for sarge-LVM2 people to become etch-LVM(n>1) people.
> I hope this is a usefull contribution and not just a brain dump!
> Alex Owen
> Debian User and SysAdmin


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