From the manual:
7 Special considerations when using multiple hard drives
Software and hardware of your system are prepared for using up to 7 hard drives. Formatting and partitioning must be done with the included installation software.
The second drive must be jumpered to 'unit 1', the third to 'unit 2' and so on. In addition you'll need a 50 pin cable between controller and drive that carries two or more connectors.
Be aware that - according to SCSI rules - terminators should only be present in the last drive on the cable. Please remove terminators from all drives but the last! When only one drive is connected the terminator stays in place.
To accelerate booting, you should install the drives with growing unit numbers, starting with '0'. If you're experiencing problems when using multiple drives, you should try different ordering of the units. Some drives cause unwanted effects to the bus which can be resolved by correct positioning [?]. If you have set up a drive, but currently don't have it connected (because of defect, noise, missing cartridge) your system will wait forever when trying to boot. To get out of this, you can press the 'Help' key and the system will boot with all drives previously found.
To set up additional hard drives:
1. Boot from the included floppy disk. Press the right mouse button, especially when you want to remove one or more drives from the system.
2. When asked 'Welche Unit möchten Sie jetzt installieren?' [Which unit do you want to set up?] choose the one to be installed.
3. Install the drive as described in chapter 5.
I hope this helps a bit...