Persistent overlay?

[Rahul Sundaram <sundaram fedoraproject org>]

Hi,

I suggested to Luke to use something better than "persistent overlay" to 
describe the amount of space alloted for storing software changes and 
settings in a Live USB.

http://lewk.org/blog/liveusb-creator-2.4.html

I am not really sure what term to use as a replacement. Any suggestions 
dear word smiths?

Rahul