Paritions to install Ubuntu

[Johann Spies]

On Mon, Oct 02, 2006 at 09:09:48AM +0200, Alan McKinnon wrote:
> LVM is a marvellous tool, designed to solve a horrendous 
> problem - physical partition sizes end up being fixed at 
> install time (for all practical purposes) and it's very hard to 
> change them. It can be done, but it gets to be like a Rubik 
> cube or that 15-pieces kid's game. LVM gives you a *virtual* 
> partition, so instead of a /dev/sda6 you get a /dev/vg/home. In 
> use, the LVM acts exactly like a physical partition except that 
> you can change it's size dynamically (to reduce the size you 
> need to unmount first though. Not so to enlarge ext2/3 or 
> reiser3). I dual boot two OSes on this notebook, both use LVM 
> and it works seamlessly. Install it, use it and mostly forget 
> about it till you need to change partition sizes.

Be careful!  LVM has bitten me more than once.  I think one has to know
the limitations of LVM very well before trying it out.  Planning is
crucial.  

Example 1: I recently did two installations using LVM.  In one case I had
a 250G disk so I used a small /boot partition (ext2) and the rest LVM.
Later I wanted to free some space for a separate partition to experiment
with Xen.  I could not do it.  To make resize a logical volume it must
not be mounted and it was my root filesystem!  So I tried using a live
cd, and then I tried to use parted to make the partion smaller and it
could not.  Cfdisk would not handle the partition at all.  With fdisk I
deleted the partition, and recreated it from the same starting point and
made it a bit smaller.  I then tried to resize the lvm-pv and logical
volumes without success.  I thought I have followed the LVM-guidelines
to resize the partion.  In the end I had to reinstall my whole system.

Example 2: I installed a system also using lvm and this time I thought I
would be more clever:  I have defined different logical groups on the
same disk.  In the end, my planning was wrong and I could not add
logical space from one group to another.  I had to solve my space
problems with symlinks. 

I do not blame LVM for my mistakes, but LVM is not just a blessing.
Make sure you know it well before jumping into it.  In my latest
installation I avoided LVM as a result of the above experiences.

Regards
Johann
-- 
Johann Spies          Telefoon: 021-808 4036
Informasietegnologie, Universiteit van Stellenbosch

     "Set your affection on things above, not on things on 
      the earth."          Colossians 3:2