Promise Pegasus 2 R6, New Mac Pro running latest Mavericks 10.9.2. Pegasus formatted using Promise's utility very latest firmware no possible updates left to run. One of the partitions has gone offline, disappearing from the desktop repeatedly while attached to 2 differnt machines. Tried everything listed here then ran DiskWarrior. DiskWarrior did an unnecessary directory rebuild but at the very end it said it changed the partition from “hidden” to “visible”. I asked the guys at DiskWarrior if I could run just the part that changed the visibility instead of the whole show. They gave me this sudo command to run any time it went goofy and so far it’s brought it back every time. CAUTION!!!
This is a sudo command so if you use it wrong very bad things can happen. Back up everything if possible but we’ve never lost a thing.
Open terminal and at the command prompt type:
sudo chflags nohidden /Volumes/Drive
BUT replace the word “Drive” with the volume or partition's name that’s offline. Then hit return.
The password: prompt will pop up, take a deep breath and type your admin password and return. The drive should show up on the desktop without having to restart or even restarting filesharing if its running Server like ours. The drive on client computers was immediately changed from grayed out to good and usable. Joe at Promise referenced this command in my conversation with him. The only thing I need to learn is scripting this so it fires off every time the drive disappears or every half our all day long on its own. Once again this worked on ours and may not work on yours. Use at your own risk. This could blow up your house and turn your kids into mushrooms. Please feel free to dispute the validity of this post I don’t care, It works for us and is our only hope of getting work done until Apple and it’s “trusted" partner Promise get in a room and don’t leave till they fix this fiasco.