My iMac backups that are stored on an external USB drive are suddenly not being recognized for backing up. Using option key and pull-down menu, I can select the set of backups on this USB drive and can restore from them, but I cannot get Time Machine to use that folder for more incremental backups — It wants to create a brand new backup (for which there is not room).
I have deleted the file /Library/Preferences/com.apple.TimeMachine.plist and rebooted the iMac, but the problem persists. I think the cause may be related to my very brief use of this USB backup file with Migration Assistant to put files onto an external hard drive: that drive now seems to be linked to this backup file in the Backups.backupdp folder.
How do I change that? I have discussed this at length with Apple support but was given no really useful advice.
Best Answer
The answer turned out to be very simple. In the command for tmutil I had copied the format and so I typed "[-a]" when I should have typed "-a". The error message always gave me the impression that the addresses were not correct. The proper error message should have said I should not include "[" or "]"