Found the solution, and that is that both system will mount the drive simultaneously in a potentially data corrupting manner.
Source: Macintouch Reader Reports FireWire: Connecting Drive to Two Computers
Q: Vy Tri Truong
I have a stack of 2 FireWire Hard Drives next to my Mac Mini. I also have a PC laptop that I sometimes use to access the drives. My Windows XP PC has MacDrive 6 installed which allows it to recognize Mac formatted discs (which these drives are). On one of occasion, I accidentally left the drives plugged into the Mac while connecting my PC to it. I found that both computers were able to access files and write to the discs.
Is having 2 computers access the same hard drive simultaneously advisable?
Turns out it is not a good thing to do, may cause data corruption, according to the same source.
A:Daniel Figucio
Is having 2 computers access the same hard drive simultaneously advisable?
No, it is not advisable in this configuration at all. The file systems on the drives are not concurrent file systems. This means that the PC has no idea where the Mac may have written data and vice versa - which means that they may both try to write data to the same block on the disk because they think it is free, when the other has already written data there - which will obviously corrupt data. The Mac and the PC WILL NOT communicate and tell each other what they have done. So use at your own risk..
...
