Sleep for the insomniac Mac

Is your Mac waking up from Sleep unexpectedly? For some this may be an increasing problem when running under Snow Leopard. A Mac developer points to the answer: a change of behavior in the Energy Saver preferences pane. The problem was pointed out in the blog of Dave Nanian, founder of Shirt Pocket Software (the maker of SuperDuper!, my preferred cloning backup software). He said that recently his Mac had been waking unexpectedly. He would put it to sleep and then an hour later, it would wake with the screen off. He found an Apple Support Document covering a new Energy Saver feature in Snow Leopard, called Wake on Demand. Here's the rundown:

With Mac OS X you can share your music, printers, files, and even your screen with other computers on your network. Previously, in order for items shared by your Mac to always be available, you had to configure your Mac to never go to sleep. With the new Wake on Demand feature in Mac OS X v10.6 Snow Leopard and an AirPort Base Station or Time Capsule, you can see and access shared items even if that Mac is asleep. This helps you save energy and reduce costs while still ensuring full access to all your shared files and devices, even remotely across the Internet.

How does this all work?

Apple says that the feature "partners" with a service called Bonjour Sleep Proxy. When a someone wants to access the shared device, the Bonjour Sleep Proxy tells the Mac to wake and do the job. Then it tells the Mac to go back to sleep at its regularly-scheduled time as set in the Computer Sleep section of Energy Saver. Now for Nanian, his Snow Leopard Mac hadn't been doing that. Until ...

Mine hadn't been doing that, but I recently reset my Energy Saver preferences to their defaults, and that turned on "Wake for network access." When that setting is on, this behavior takes hold. And if you Mac doesn't go to sleep on its own (for whatever reason), it stays on after the first wake.

Nanian said that turning off Wake for Network Access resolves the issue.