[linux-lvm] moving logical volumes online

[Vijay Sundaram]

Hi,

I had the following questions:

1. Linux lvm has snapshot capability, but to make sure that all changes to
a logical volume have propogated to secondary storage it is recommended
that the logical volume be unmounted before the snapshot is taken. Is this
absolutely necessary?

2. The second question is regarding moving or migrating a logical volume 
from one volume group to another when the logical volume is online. 
	Taking snapshots allows one to create a backup, but my question
then essentially is: if one creates the backup on another volume group,
can one bring this backup up-to-date with any changes that may have been
made to the primary copy. I can then make this backup the primary copy and
delete the original copy.
	Of course, it is required that the logical volume be online and
functional (available) at all times.
	Does lvm have this capability, or does it already achieve it in a
transparent way?

thanks,
-- Vijay