A bit ago I covered my plan for a comprehensive backup plan for my Mac. I thought when OS X Mt. Lion (10.8) came out that being able to use 2 Time Machine drives would fix my, one-in one-out, process. However it did not. When you swap back in the drive that’s a month out of date it still doesn’t always pickup where it left off, and to add to that you get a notice every couple days that the other drive is unavailable for backup. So 1 drive at a time is best in my experience.
After swapping the drives most often it freaks out saying the drive is full and seems unable to actually do house cleaning or pickup where it left off. My guess it regards the drive a new backup not a continuation. So I find it best to start anew each month. After swapping the drive, follow this procedure to wipe the newly back in service Time Machine drive and start off a fresh new month of back up data.
Correct swap in a new Time Machine drive that has been used before:
- Stop using the backup drive in Time Machine: Open System Prefs, Time Machine, Select Disk, Click the disk that is active, ‘Remove Disk’. Confirm ‘Stop Using This Disk’.
- Stop time machine: Open System Prefs, Time Machine, click the big ‘Off’ switch.
- Eject the Volume (if it won’t eject, see “Force Eject Time Machine Drive“)
- In Disk Utility: Erase drive, “Mac OS Extended (Journaled)” Erase.
- Then remount the drive with disk utility and turn back on time machine, you’ll have to reselect your drive, and let it rip.
Terminal: hdforceiutil eject -force [drag drive here]