This isn't a request for help but an FYI in case anyone else comes across this. A NW6.5 BorderManager server I had was getting SYS volume out of disk space errors even though it was nowhere near full. I rebooted the server and then I noticed one of the mirrored drives had died and the server wouldn't mount SYS.

I removed the dead drive and the server would boot without the drive deactivation message, but would not mount SYS. I loaded NSSMU and the NSS partition containing the SYS pool and volume had no pool associated with it. I was sure I'd be reloading the server, but I played around a bit and solved the problem.

I first went into the RAID devices menu and removed the dead drive from the mirrors. This didn't solve anything, but I noticed the devices did not show 100% remirrored. I hit F6 to restripe the array and the volumes went to 100% remirrored and the SYS pool appeared again. Day saved! Hopefully this may be useful to someone else down the road.