Persistent images: how to make diffs of it?

[hotplainrice]

hey guys,

persistent images are so great now and i have multiple backups of them, 3.7GB each ( i know its big).
i just cp them to a different name. you guys know any better method?

Tried xdelta but got an error
knoppix@1[sda2]$ xdelta delta ./knoppix.img.bak ./knoppix.img patch
xdelta: stat ./knoppix.img.bak failed: Value too large for defined data type

Thanks. :)