Retro fit an old Server with an Adptec 1200 Raid

In order to increase disk capacity and implement Raid 1 on an older NT4 server I would like to install an Adaptec IDE raid card. I installed the card and connected the old (9G) hard drive to the primary and the 1 of the new (100G) hard drives to the secondary. The mirrored set was created but upon reboot the system crashed. I believe the problem was in the arc path but I am not sure. I reconnected the old (9G) drive to the onboard IDE controller and booted successfully.

As far as I know you must have identical size hard drives when implementing raid. Both need to be 9GB.