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geo88

macrumors member
Original poster
Nov 19, 2019
53
26
Nashville, USA
There is about 560GB used / 440GB free on my 1TB startup volume. Time Machine backup fails with an empty 1TB USB hard drive, saying 1.13 TB is needed.

Works fine with a 750GB internal hard drive and says only 613GB is needed.

Running the latest Mojave on a Early 2009 Mac Pro. My internal drives are APFS. The external is HFS+. Could this be the issue?
 

Honza1

macrumors 6502a
Nov 30, 2013
933
433
US
There is about 560GB used / 440GB free on my 1TB startup volume. Time Machine backup fails with an empty 1TB USB hard drive, saying 1.13 TB is needed.

Works fine with a 750GB internal hard drive and says only 613GB is needed.

Running the latest Mojave on a Early 2009 Mac Pro. My internal drives are APFS. The external is HFS+. Could this be the issue?
I wonder. Is the internal TM disk removed from TimeMachine? Looks to me TM is trying to backup both main drive and the internal TM drive.
By default all internal disks are added to TimeMachine backup and all external disks are added to Excluded list. Make sure the internal TM is excluded from TimeMachine backup.

All of my TimeMachine disks are HFS+. I am surprised that you have TimeMachine disk (inetrnal) which is APFS. I thought that you cannot use APFS for TimeMachine, since APFS did not support hard links yet.
 
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geo88

macrumors member
Original poster
Nov 19, 2019
53
26
Nashville, USA
I wonder. Is the internal TM disk removed from TimeMachine? Looks to me TM is trying to backup both main drive and the internal TM drive.
By default all internal disks are added to TimeMachine backup and all external disks are added to Excluded list. Make sure the internal TM is excluded from TimeMachine backup.

Thanks for your help, Honza1. It does seem that Time Machine somehow became confused. Still not sure why it failed when backing up to the external disk, but was ok with the internal one. I could not fix it via System Preferences, but deleting Library/Preferences/com.apple.TimeMachine.plist and restarting made the problem go away.

All of my TimeMachine disks are HFS+. I am surprised that you have TimeMachine disk (inetrnal) which is APFS. I thought that you cannot use APFS for TimeMachine, since APFS did not support hard links yet.

I was mistaken. It appears that Time Machine reformats as HFS+ when it erases the disk. Thanks again.
 
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