[Guvante]

Assuming you don't have it protected, you need to be more cautious than that, as the file system is not simply a long stream of bytes.

[hackinthebochs]

Very true, my numbers were just an illustrative example given the context set up by the comment I replied to.

[fuzzbang]

Which you apparently didn't read thoroughly. I clearly state that the secure way to use TrueCrypt is to never mount the hidden volume in protected mode. That will enable the scenario you describe. I even state the reason why you want use it the way I suggest is to minimize the amount of hidden data that is overwritten.