What are the advantages of LVM?

[Kent Borg]

I have played with LVM a little, and it is a bit confusing, and though
resizing is cool LVM can't magically eliminate the need to resize the
ext3 or Reiser or whatever filesystem you have stored on LVM.

However there are two features it has that I haven't seen mentioned in
this thread (but I might have missed it).

 - The ability to make instantaneous snapshots of a file system.

Making a backup onto tape or disk takes time.  From the start to the
finish of the backup the data being copied can easily have changed
enough that the backup is not self-consistant.  With an LVM snapshot
you know it is self-consistent, now you can backup the snapshot
without worrying about racing ongoing activity.

 - The related ability to have multiple filesystems that are similar
   to each other, and only store the common data once.

This interesting when playing with things like Qemu, Vmware, and Xen,
where you might have multiple virtual Linux machines running (or not
running) at once.  Storing only how they differ from each other can
save resources.  I think both disk and runtime.


Admittedly I am not an LVM expert (and I hope I got the terminology
above close) but these are some of the reasons I am interested in it,
and why I have it on my notebook disk.


-kb