[BBLISA] Backing up sparse files ... VM's and TrueCrypt ... etc

[Edward Ned Harvey]

Just by looking up deduplication on Wikipedia, I found a few interesting
points:

* typically, they use weak and strong hashes, where the strong hash isn't
even calculated unless there's a match in the weak hash.

* most vendors use very strong hashes, to the point where statistically,
hardware failure is a larger source of corruption

* in the most extreme cases, a bit-for-bit comparison can be made, to
confirm beyond any doubt that the two chunks of data match, after the two
hashes have matched.