I have several 3,4 and 5TB WD Green drives that I've always disabled the head parking timer on with the WDIDLE3 utility. I've never had an issue, however I just acquired a 6TB WD Green drive (WD60EZRX-00MVLB1) and when I use WDIDLE3 on it, I can read the current timer is set to 8 seconds, however if I try to disable it just doesn't work. I type the command it and it does nothing. Trying to set the time to another value like 300 seconds does the same thing. I've tried doing it on other PC's and even with different boot CD's with WDIDLE3 and all have the same results.

Anyone have any ideas what this is or seen it before? Is this just something with the newer 6tb green drives? I'd prefer not to keep the timer at 8 seconds since I've already had 100+ head parks in less than a 4 hours.

maybe the APM (Advanced Power Management) is disabled
someone had the same problem lately with a Seagate drive...
read here