This is called a known plain text attack. Most modern algorithms are hardened against this. So this technique wouldn't help unless the algorithm had a known weakness to this. But then again, maybe people still encrypt their archives using enigma machines these days. The world is a crazy place.

This doesn't apply to ZFS due to the way it uses drives. All drives are added to a storage pool, and drives are used as needed based on speed and reliability requirements. So to upgrade, you'd just add a new drive to the pool, mark the old drive for removal, wait as it moves the blocks to any other drive(s) in the pool, then remove the old drive.

But the money goes into their ad sense account to spend on more adwords. It doesn't cost them anything, as it is a check written to them selves.