I have a macbook pro laptop using mountain lion. I just setup time machine onto a WD My Passport and it worked fine (took about 2 hours over USB 3.0 for 333 GB of stuff). My question is, given its a laptop, i will not have the external hard drive plugged in all of the time. Is there anything i need to worry about with regard to Time Machine config, etc given the fact that i won't have it plugged in all of the time.

If i skip a backup cycle because the hard drive is not plugged in, does it kick off right when i plug it in or when the next scheduled backup gets kicked off? Lets say I don't plug in the hard drive for a month. Does it queue up all of those backups or just start from where I am at when I plug it back in?

2 Answers 2


Time machine keeps a local store of backups if the time machine drive is not available. This is transferred to the backup drive when it is next connected, so you don't even miss an hourly save. You can see these highlighted in a different colour if you enter time machine a few hours after being disconnected from the backup drive.

Source: http://support.apple.com/kb/HT4878


If Time Machine misses a scheduled backup, it will start one the next time you plug in the external drive. In my experience it sometimes takes a few minutes before the backup starts.

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