Automatic Vs Manual Sleep Issue

I'm having a strange problem with sleeping my Mac Mini.

If i let the computer automatically sleep then the 2 external drives spin up and down continuously.

If i sleep manually apple: > Sleep) then no such problems occur. The drives spin down, and stay down.

Any ideas as to why this happens and how to make automatic sleep replicate manual sleep? why are they not identical?

Matt.H said:

Have you double checked your settings within System Preferences?

Under "Energy Saver". Could it be possible it has been set to put the display to sleep, before the computer (therefore the hard discs would continue to spin). Also check that the box titled "Put hard disc(s) to sleep when possible" is also checked.

Click to expand...

Previously yes the display slept before the computer did (10 minutes before, to be precise). However, whilst testing the sleep discrepancy i set computer sleep to 1 minute, whereby both display and computer sleep simultaneously.

Also, whilst the display sleeps the external hard drives spin at a constant rate. It's only when the computer sleeps that the disks ramp down, and then back up: repeating this process in a continuous and perpetual cycle. It's as though they almost finish their unmount before being asked to mount again.

And yes this occurs with "Put HD's to sleep when possible" in either state.

What i particularly don't understand is the discrepancy between manually instigating sleep and the automatic mechanism. Surely the protocol should be the same - though evidently that is not the case ..

Does anyone know the technical differences between the two mechanisms? Knowing this difference will surely elucidate the cause of the problem.