True64 4.0g - Change of system disk

Hello Admin Wizards,

I just installed a "new" (hrmpf...) 9 GB Disk into our backup server. I 
plan to use it as "system disk" to get the rest of the raidset free of 
the system and keep it clean for data.
At the moment, the system resides in two advfs partitions : MYLEX#root 
and MYLEX#usr, mounted as / and /usr.
I mounted the disk as /mnt.

Now what would be the easiest way to copy simply everything from those 
two partitions into /mnt to have a bootable new disk?

I have considered three different solutions:
the use of cp .... i will refrain from this for obvious reasons ;o)
the use of rsync
or simply a tar cfv / -T -  | (cd /mnt ; tar xfvp -)

Question: did I miss the best method? Or would it be easier anyway to 
set up the system from scratch?

thanks for any hint
CW