2009 iMac with home-made Fusion drive: keeps sleep/wake cycling


macrumors regular
Original poster
Aug 4, 2003
New Jersey
I have a 2009 iMac into which I self-installed a Fusion drive, using widely available instructions (about a year ago I guess). I waited until the Mountain Lion update came out that had full support for self-made Fusion drives.

Everything works great except one thing: sometimes, when I put the machine to sleep, it wakes up a second later, does something briefly, and then goes back to sleep. This might happen several times before it finally stays asleep. Just now, it happened like 20 times and that led me to post here.

Although I have no direct proof, I can't help thinking that the Fusion drive installation is what started this problem. Anyone ever heard of this, or know a way to diagnose it?


macrumors 6502
Apr 14, 2012
You might want to check your system preferences under energy saver and make sure "Wake for network access" isn't checked.

We have several systems with both Apple and company made Fusion drives and they don't do that at all. Possibly another process is waking the system up before it's fully asleep.


macrumors 6502a
Apr 28, 2012
Open up a terminal session and type pmset -g assertions

This will tell you what processes are keeping your Mac awake, so you can do some further investigation from there. Common culprits are external USB devices with badly written drivers. My Pioneer BluRay USB BluRay drive for example prevents my iMac from sleeping.

I am 99.9% sure it has nothing to do with your Fusion drive.


macrumors regular
Original poster
Aug 4, 2003
New Jersey
Well, naturally after I posted this I haven't had the problem again. I didn't change or unplug anything. Here is what my pmset -g assertions looks like:
Assertion status system-wide:
   BackgroundTask                 0
   PreventDiskIdle                0
   ApplePushServiceTask           0
   UserIsActive                   1
   PreventUserIdleDisplaySleep    0
   InteractivePushServiceTask     0
   PreventSystemSleep             0
   ExternalMedia                  1
   PreventUserIdleSystemSleep     1
   NetworkClientActive            0
Unfortunately until I experience the problem again I can't diagnose it. If it ever happens again, I'll post back here.