to repeat what Berion has already explained (in case you are still doubtful)
The ps3 encrypts the hdd using a value unique to that console.
When you put it in another console, it will look like gibberish because it is trying to decrypt it using a different key (unique to the 2nd console).
There is a clone hdd feature in the rebug firmware (and dex firmware) that is supposed to copy absolutely everthing to a new hdd. The new one must be at least as big as the current hdd.