What are the advantages of LVM?

[David M]

A friend very kindly gave me his old computer which had been sitting around
gathering dust for a few years, and so I decided to install Ubuntu on it.

Out of curiosity, I decided to (attempt to) format the hard disk using
LVM, but I found the whole experience very confusing, and I'm afraid
I'm not sure if I could see the point in it..? (using Dapper Beta release)

The LVM setup decided to set up a volume group for /, and another one
for swap, each of which contained a partition for / and swap
respectively. This was followed by stern warnings about how these were
permanent group settings which could not then ever be changed.

So, I decided to try to split / into / and /home, but found I was unable
to do this: I couldn't resize the / partition (which is what I thought
was the point of LVM?), so I'm a bit perplexed as to what I would
actually have gained with LVM: I thought it was supposed to allow more
flexibility in resizing partitions?

After some tussling with the disk partitioner, I finally managed to
eradicate all traces of LVM (it seems a bit hard to remove once the disk
has any sign of it ever having been there) and just partitioned the disk 
normally. (This is not really a major issue as I was just trying to
experiment, but I'm curious as to how I should use LVM properly, and
what I would gain from doing so).


Unfortunately, once I did partition the hard disk, I forgot to mark / as
bootable, and so I can't boot from the hard disk directly. Luckily the
install CD's "Boot from hard disk" option rescues me from this mistake. :-)
Is it possible to now subsequently set the bootable flag on the / 
partition without having to reinstall the system or trash the existing
partition?


Thanks for any advice,


David.