Time Machine Backup is failing to 2nd Drive
I have been using Time Machine with a pair of USB attached drives for several years now without a problem. The drives have changed over that time as space requirements have changed, but the current pair have been my Time Machine drives for quite some time. I am running macOS Mojave 10.14.2. I have been backing up both my internal SSD and an external SSD. The drives I am using for Time Machine are Western Digital My Book 6TB. The external SSD is a Western Digital Passport 1TB.
Of course I bought my MacBook Pro in Dec. 2015 so my extended Apple Care coverage expired a few weeks ago.
This past week, backups failed to one drive (Mospheira), then the other (Hogwarts). In both cases the backup would start with many gigabytes backed up prior to failing. I did some research and found a command to search the logs for errors and the failures appear to be permission related. The command I am using is "sudo log show --predicate 'subsystem == "com.apple.TimeMachine"' --info --last 4h | grep Error". The output appears at the end of my post.
My next step was to boot into recovery mode and run a verification on my internal drive. I also ran File Aid on the external SSD. No issues were found with either drive. I removed both external drives from Time Machine and added them back. I also ran File Aid on the time machine drives and found now errors.
Now the first drive (Mospheira) works fine. But the second drive (Hogwarts) fails with the same errors as before. When I remove Mospheira from the Time Machine list and only have Hogwarts for backups, the failure still happens. I replaced the second drive with a brand new WD My Book 6TB drive and it fails with the same errors. Mospheira continues to work for backups.
I used Onyx to clean up system cache. This has fixed some odd problems in the past but did not make a difference this time.
I have reformatted the drives that Time Machine fails with multiple times per Apple's instructions and it doesn't make a difference. I excluded the external SSD from backups and Time Machine still fails. At this point I have been running for several days with only Mospheira defined to Time Machine and backups work every time.
Adding the log output to this post will exceed the 5000 character limit, but I have it saved.
MacBook Pro Retina (2015 and later)
