LTO 3 or 4 drive and tapes seem to be winning out on the archive method, they are pretty fast and good $/GB and a lot more secure than BU to hard drives.
Easy way to think about the RAW P2 files is to think of them as tapes, if you would keep the tape if it was shot on it, you would BU to LTO the RAW footage, this way it can be transfered into any NLE down the road.
There are several post that do into it more but that is my take on it.