I've been regularly backing up my 2011 MacBook Pro using Time Machine with two separate external drives (1Tb at work, 2Tb at home) while running Mavericks.

Today I upgraded to Yosemite, and Time Machine seems to think I have a brand new computer - the backup on the 1Tb disk failed with "not enough space", and the backup at home is currently attempting to back up the entire 350Gb on my computer.

(Previously with the 1Tb drive, Time Machine would automatically delete old archives when the drive was full.)

Is this a common problem (ie a bug)? Is there a way to tell Time Machine to continue where the last backup finished, rather than starting a brand new "branch"?

  • was it a clean install, or a simple upgrade in place? Clean install would make it consider it a new computer.
    – Tetsujin
    Commented Oct 27, 2014 at 14:55
  • @Tetsujin it was a standard upgrade, made via > App Store > Updates Commented Oct 27, 2014 at 22:20
  • 1
    I ended up reformatting both external disks due to an unrelated issue, so I never resolved this. It would be interesting if anyone knows a less destructive way to solve the problem though Commented Oct 29, 2014 at 23:00

2 Answers 2


You may want to check this thread: https://discussions.apple.com/message/27031297

It seems that if you backup external drives with Time Machine and you disconnect them at a later point, for instance for a few hours or days, and reconnect them, Time Machine will want to make a full backup of them (even if nothing has changed). That behavior appeared with Yosemite. I have not heard about any solution or workaround (yet).

  • That sure sounds buggy to me - maybe reformatting was the quickest way after all! Thanks for the tip Commented Nov 5, 2014 at 19:58
  • ... even reformatting didn't help, as alluded to in the post you linked to. It looks like Yosemite has a bug when backing up to multiple drives? I've resorted to running Time Machine on the 2Tb drive and Crashplan on the 1Tb drive. It's probably safer to spread the backups over 2 programs anyway Commented Nov 16, 2014 at 23:12

There's some coding in Terminal you can do to remove flags osx or os sierra applies to those TM backups, then retry TM again. You can try repairing the sparsebundle files in recovery mode (backup current iteration in addition to the SB to an HDD to be safe).

  • 2
    Welcome to Ask Different! This answer appears incomplete: what 'coding in Terminal'? According to How to Answer, all answers should try to be complete and self-contained so others can find them by using the search feature. Please update your answer to include the missing info to make your answer complete.
    – fsb
    Commented May 9, 2017 at 17:17

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .