I'm afraid the quickest and safest way seems to me to take a full backup, replace the disks, make a new RAID-set, and restore. It'll cost you a night or a sunday, but there is no easy other option. You could for example replace the drives one by one, and let the rebuild take place (as if you replaced defective drives), but in that case only 4.3 out of the 9 GB of the new drives would be used.
Depending on your RAID-controller, available space and so, you could add the disks and simple createa new RAID, but copying/moving data is trickier than simply replacing the disks.
I would do this:
-Make a GOOD reliable backup.
-Double check that backup!
-Login via a workstation
-On the server: LOAD DSMAINT|Backup NDS prior to hardware upgrade.
-Copy that file to your workstation.
-Remove your disks (keep their order, just in case...)
-Install the new disks.
-Boot from the SmartStart CD.
-Select the Array Configuration Utility, and let the wizzard guide you. The defaults are "all disks", "all space" and "RAID5".
-Install NetWare in a temporary tree.
-Log in from the same workstation, and copy the backup file to SYS:System
-on the server, LOAD INSTALL|Directory Options|Remove Directory Services
-on the server, LOAD DSMAINT|Restore NDS after hardware upgrade.
-Install the backup-software.
-Restore.
Good luck. Prepare for sandwiches..:-)
Jim