LVM on a laptop

[Paul Howarth]

William John Murray wrote:
>    Hello all,
>             I just faced a laptop problem: How to shrink the FC4
> allocated space in order to increase the space on another operating
> system. I had used the default LVM. 
>   A trusty knoppix liveCD QTparted knows nothing of LVM, so I tried the
> FC4 rescue. After a long time, I found:
>    * resize2fs shrinks the ext3 / area. OK
>    * lvm lvreduce shrinks the logical volume (different units)
>    * lvm pvmove allows me to put all the lvm handled stuff physically
> together. More different units.
>    * vgreduce...fails
>  
>   I think I was supposed to use vgreduce to shrink the space managed in
> the volume group - but I couldn't make it work. It only seems to delete
> logical volumes.
>   Finally I reversed all the above operation. Since they are all in
> different units, and I had padded a little to be safe, I had to pad
> some more on the way back, and now I have wasted space.
> 
>   Two questions:
>   *) How could I have made it work?

There is no straightforward way of shrinking an LVM physical volume that 
I know of. I think you need to have some way of shifting all of the data 
off that volume to somewhere else (e.g. backups, another disk), delete 
the volume and then create a new, smaller one.

>   *) What benefit is there in lvm on a laptop, when you pretty much know
> there will only be 1 disk?

In the default configuration of one big physical volume and one logical 
volume for the whole system (exceot swap), there's not a lot of benefit. 
However, if you configure it manually and use multiple volumes so as to 
keep for instance the /, /var, /usr, /tmp, /home filesystems separate, 
and/or you don't allocate all available disk space to the physical 
volume, then LVM has benefits in that you can reallocate space usefully 
later on. Just don't create a physical volume that you may need to 
shrink in the future - it's better to create something too small and 
then add to it when necessary,

Paul.