[G4] Firewire problem

[Sims David]

Hello,
I have two G4 gigabits networked via firewire.  Computer A has an  
external firewire drive wired to it, that is used by both computers  
for backups. Computer B accesses the drive by connecting to A and  
mounting it.

Here is the problem....

Often times, the external drive disappears from computer A's desktop.  
It does not show in the drive utility, but it does show up in system  
profiler. Even when it is not accessible from computer A, computer B  
can mount it and use it.  If the firewire cord is unplugged and  
plugged back in, the drive appears on computer A's desktop.

Is there a way to get the drive accessible, without unplugging/re- 
plugging the firewire cord?
Thanks,
David