[linux-lvm] Snapshot sizes

[Gashaw Teshome <gasht neopets com>]

I would like to use snapshotting to backup an LVM-based machine.  The files 
that I want to backup total about 20G, while LV is about 100G.  What size do 
I need to make the snapshot volume to allow for this much data?

Please let me know if I need to add any more information to make myself 
clearer.
-- 
Gashaw Teshome
System Administrator
Neopets.com