When your external disks are not willing to go to bed...

We've had problems with our iMacs bed time in the office pretty much since we started using them.

At night, they seem to refuse to fall asleep.

We've tried all the possible settings provided by the OSX interface. But nothing worked. Until I realized that the problems seemed to be related to the external back-up disks attached to them.

We use a LaCie and a Western Digital, both with a 1TB capacity, respectively connected to a first generation 24" Intel iMac and to a before-the-latest generation 27" iMac.

1. Sleep settings don't work for the hard disks
   
2. Manually unmounting the disks seems to solve the issue, but mounting them back is not trivial
   
3. OSX seems to unmount the disks when I log out from the Apple menu but when I log back in I have to restart all my applications
   

I have found a solution that requires the use of the "Fast user switch menu". The settings are as follows:

1. Go to System Preferences > Accounts
   
2. Check "Show fast user switch menu as" and choose the option you prefer
   
3. Make sure the "Show the Restart, Sleep, and Shut Down buttons" box is checked
   

Now, when you want to put the whole system to sleep, the solution is:

1. Click on the Fast user switch menu (top right of your screen)
   
2. Call the "Login Window..."
   
3. Press "Sleep"
   

Et voilà !

My guess is that the sleep option from the login window actually unmounts the hard disks and leaves them inactive until you enter your account again.

As a side note, those sleep problems also had a disturbing side effect: when I'd simply put the system to sleep the "old" way (either by calling "Sleep" from the Apple menu or by using the automation settings in "Energy Saver"), and tried to wake it up in the morning I'd have what looked like system freezes that sounded (yes, actually "sounded") related to the external hard disk activity. With the new system, I've had only one case of "freeze" in a few weeks of time, and it still kind of looks related to the external disk behavior.

In any case, this system seems to be allowing our Macs to spend their whole night sleeping and not struggling with hectic external disks... I'll need to check further what is the cause of the disks' inability to sleep, and also what is the cause of my freezes (not happening on the 24"), but that's for another post...