You could build a seperate raid with the new drives and leave the current one as it is. Otherwise you’ll have to move your footage off the current raid before building a new one with all the drives.
Actually, after looking at it again, it looks like it will record 63 minutes in the 1200A and 126 minutes in the older model machines like the 150
The newer decks are the ones that can record longer and the older ones will only record 31 minutes in DVCProHD. The newer decks have 9 micron heads versus 18 micron heads on the older ones so they can fit twice as much data on the same tape.