OS X Lion no longer wakes on lan to share external drive
I have an Air and a Mini, both running Lion. The Mini has an external hard drive connected that it uses for Time Machine. That hard drive is also shared on the network so that the Air can automatically mount it and back up to it as well. This was working great under Snow Leopard, even automatically waking the Mini to share the drive as necessary.
After installing Lion, the Air's backup only works if the Mini happens to be awake already. If the Mini is asleep, the Air gives an error: "The backup disk could not be found."
The Mini is connected by wire to the router, which the Air connects to wirelessly. The Mini is set to wake on LAN in its preferences, and the Air automatically mounts the drive when it is available, just not when the Mini is asleep. How do I make sure that the Mini wakes up properly for file sharing?
Mac mini, Mac OS X (10.7.1)