We had a problem at work in which a shared FireWire drive would unmount when logging out of a user account. This is unfortunately the default behavior under OS X, and there is no easy preference to turn it off. This default behavior is intended to prevent inexperienced users from unplugging a device after they log out, naively thinking it is safe to do so. However, in a network setting when you want a drive to remain mounted persistently, because it is a shared resource, this presents obvious problems. If someone logs out on the computer with the FireWire drive, all network connections are terminated, and anyone trying to read or write to the drive will be rudely cut off, possibly resulting in data loss.
I was happy to find a workaround, and it is pretty simple. Open the Terminal application (in the Utilities folder), and type all on one line (no line breaks):
sudo defaults write /Library/Preferences/SystemConfiguration/autodiskmount AutomountDisksWithoutUserLogin -bool true
You must do this from an administrator account, and you will be asked for your password. Then restart, and you should have no more unexpected unmounting. I have tried this only under Tiger (10.4), but someone said in a forum that it works under 10.5 as well.
Seems there’s a freeware app for this somewhere. It was quite a while ago that I saw it. Can’t recall the name of it though.
Daniel