On 10/28/2012 03:06 PM, Michael Kjörling wrote:

You_can_  calculate a worst case
scenario figure (no compression possible on the new payload data), but
that's about it.

Well, there are those humorous edge cases where you compress a tiny 
amount of uncompressible data, and the "compressed" version ends up 
being larger. Not sure if that applies to the specific algorithms that 
btrfs uses, but I've seen it happen with tiny datasets before. Even 
worst case could be hard to get right perhaps!

-- 
R