As spiffy as Mac OS X’s 10.5 Time Machine feature can be, a number of users have noticed that their external hard drives continue to spin even when they have stopped using the drive, which has brought about the question as to whether the drive was being accessed by another, unauthorized application or because of a bug. While this issue does not have a clear solution, most people agree that the disk access is normal and not a result of a bug.
According to MacFixIt, users have submitted the following comments, workarounds and ideas:
Apple Support Discussions user “Timothy Arends1” commented:
“I have an external LaCie FireWire hard drive that I use for Time machine. I understand that it should stay on and connected to my Mac so that time machine can make its periodic backups.
I normally do not like to leave it on, because it “cycles.” By that I mean, it will go to sleep, or “spin down,” and then a few minutes later, for some reason it will wake back up again.
When Time machine is backing up to it, it is understandable, but it “churns” even when Time machine is not using it, for example, when I simply save a file to my documents folder (I never save anything directly to my Time Machine drive) or sometimes for no reason at all.”
This was followed up by Apple Support Discussions user “Robert Weingarten”:
“Although I have turned off Time Machine in the Preference panel, several times per hour TM keeps trying to access the external FireWire HD that it formerly used to do backups. I repeatedly hear the FireWire drive rev up each time this happens and its very distracting when working at my computer. Can anything be done to completely make Time Machine forget that drive?”
Possible workarounds for the issue include controlling the frequency with which your Mac accesses the external hard drive, as outlined by user “Pondini” on the Apple Support Discussions board:
“Some drives respond to the Put the hard disk(s) to sleep … option in System Preferences > Energy Saver.”
By most accounts, it is completely normal for a mounted external hard drive to be accessed several times per hour, even if the drive is not directly in use. To get an idea of what processes are causing your drive to be accessed, you can open Activity Monitor in your Applications, Utilities folder and watch for processes to spike as the drive is accessed.
The user then suggested going to www.bivalve.net/reference/OS-X/background-processes.html and looking into the Window Server application, which manages the display and mediates how Mac OS X’s various applications and other processes that want to display information on it, as the program does the grunt work of launching new user applications.
