LVM on root [was Re: [CLUE-Tech] Moving data between partitions?]

[Keith Hellman]

--- David Anselmi <anselmi at americanisp.net> wrote:
> Keith, does SuSE use LVM for the root partition?  You make it sound like
> it doesn't.  I read (about a year ago) about someone using a pivot root 
> to make that possible.  Since I don't know how pivot root works it 
> sounded like a lot of work to set up (it was an LFS system though, so 
> probably not much *extra* work).

I don't recall if SuSE provides an LVM root option during install.  I'm
pretty sure it's possible to have an LVM logical volume as a root, but I
think it would take a slightly specialized setup.  The reason I DON'T use
LVM roots is that I want to be able to use any rescue disk/rescue kernel
possible.  If you make an LVM root workstation, then you MUST have an LVM
aware rescue kernel to do any type of repair or correction to the root
partition.  IMHO, thats too far out their in the risk zone.  If I have to
do a root fs repair, I want to be able to use whatever general tools are
at my disposal at any time.  If I need to repair something 'at a higher
level' in the boot process, I simply boot into single user mode or with
init=/bin/sh and proceed from there...

> As for other distros, Mandrake has LVM as a partition type in the 
> installer.  I know there's more to it than just setting the type, so I'm
> not sure how well it works.  I didn't try it.
> 
You are correct, it is more than that.  fdisk will allow you to set a
partition type to 'LVM Partition', but that is not enough to actually
create an LVM enabled workstation.  The SuSE install actually provides a
nice interface for
* re-fdisking your disks if desired
* associating partitions with LVM physical volumes
* allocate physical extents from the PVs to logical volumes
* format both normal partitions and LVM logical volumes to your desired
filesystem type
* designate the mount points for both normal partitions and LVs
* perform an install onto your specified configuration

If I had to use a non-LVM installable distro, these are the steps I would
take:
* install the absolute bare-bones minimal system onto a 256M partition
* get a custom built LVM aware kernel and LVM tools installed on minimal
system (since I did a minimal install, this means rebuilding the kernel on
a second workstation...)
* using fdisk + LVM tools, I would setup LVM system and fstab,
transferring over any 'relocatable' root directory contents (home, usr,
var, opt, ... )
* make sure I can boot and I have a working system
* return to the distro CDs and install an additional selection of packages
appropriate for the machines intended use (most distros have canned
server, workstation, development station, graphics station, ...
collections of packages.

Thankfully, I've never had the inclination or need to do this.  The only
non-LVM machine I run is my workstation at work (RH 7.2 <wrech>); it does
not support LVM - some day they will ask me why it's going to take me half
a day to revamp/reconfigure my machine for some development need, and I'll
tell 'cause you didn't let me use my SuSE!' :^)



=====
Keith E. Hellman
kehellman at yahoo.com

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