I have an external WD drive connected via FireWire as my Time Machine drive. Recently I have noticed that it is active at times when it is not backing up or otherwise in use. This happens even when I eject the drive (but leave it attached).
I'm concerned that this will reduce the life of this essential drive. Any idea what is happening? Is there anything I could or should do to resolve this behaviour?
macOS Sierra / Mac mini (Mid 2011)
I too have seen this behavior and had the same questions a while ago.
Here is a good read. This will answer a lot of your questions.
It’s constantly watching what ever you do and preparing for it’s hourly backup.
It also manages the backup history and deletes the oldest files when it starts running out of space.
It will last as long as any other drive you have,
Your main hard drive is doing even more, every second your computer is on.
Run ‘Console’ and watch the System Log and see all the action going on.
Time Machine: What It Is, How It Works, How to Use It with Your Mac | Other World Computing Blog
Thank you for your detailed answer. It is very reassuring to know.
My Time Machine drive keeps spinning up when not in use
