Question:
It is strongly recommended that i use two scsi disks in a external case -
can i use only one with two or more partitions on it for the "shared
device"?
Answer:
I am pretty sure that you have to use two physical drives. If you are using an external RAID, you can create two logical drives called LUN's that can be managed as if they were two physical drives. But on standard SCSI disks this won't work.

Leon

Question:
Is a separate SCSI Card needed for the External SCSI case or is this
External device just a part of the SCSI-Chain between the two nodes (the
Endpoints of the SCSI chain are the two nodes)?
Answer:
Yes the termination happens in the nodes and Termination is disabled on the external drives (or enclosure).
Question:
Is the Meaning of a external SCSI enclosure will have the Y cable built in
internally the same as the SCSI Drives of this External case are terminated
internally?
Answer:
No, See above for proper way (node termination).
The reason is that both computers (nodes) have to be on the same SCSI Bus so they can both see the drives. Then they use SCSI Disconnect and Connect to talk to the drives one node at a time.
Each time they connect, each node reads the FAT off of the drives.

Leon