We have an STK SL500 tape library with 4 LTO4 drives in it and it seems to 
randomly take all of the drives offline. STK/Sun has replaced the robot and 
controller card (more than once) and nothing seems to help. This has been going 
on for several months now and I'm at a loss to figure out what is causing it. 
The SL500 and it's drives are all attached to a Brocade DS-4900 switch. Nothing 
has changed on the switch in over a year as putting maintenance on them is a 
real chore since we have so many devices attached to it.  The only message I 
see in the act log is:
ANR8848W Drive WRLTO4-1 of library WRSL500 is
 inaccessible; server has begun polling drive. (PROCESS:
 832)
As best I can tell, it is a hardware problem as even rebooting the robot or 
power cycling  the whole box doesn't fix it. The robot stays parked at the top 
and never seems to go through the audit it usually does when it is rebooted. If 
it is indeed a hardware problem, I realize there isn't much that can be done 
but they have replaced almost all the parts in the box and it keeps happening. 
Anyone else ever have similar problems?
John