Why Time Machine failing periodically?

[wlow3]

My mother’s Time Machine periodically fails to complete a backup. (iMac 4K 2017 running latest macOS 10.14.4).

When I first looked at it I ran Disk Utility and it couldn’t unmount the disk to do First Aid. I could look through files on the TM disk but I think there was an error (error 50) that said it couldn’t write to the disk.

The external HD is a 3T WD My Book. I tried to run their utilities but none of them responded.

I saw something online about checking the preference to let drives go to sleep whenever possible, so I tried that and restarted the iMac. Backups started again. I again ran the check disk WD utilities and they all now worked and said the disk was fine.

Several days later the TM drive again reported the backup had failed. Again the WD utilities would not respond so I tried to eject the drive. It said it was busy so I force ejected it, unplugged it from the iMac then plugged it back it. Once again, WD utilities worked and reported no problems, as did Disk Utilities and the disk started backing up without issue.

Any ideas what could be happening?

 

[cruisin]

The drive cannot wake up in time for the backup to happen, hence the error.

The WD Utilities could be preventing the drive from waking up, have you tried removing the utilities? They are not necessary to use the drive so you can try using the drive for a while without them. Your machine should be able to handle sleeping and waking the external automatically. Or you can force quit the WD Utilities and see if that changes the situation.

Otherwise you can shut down or reboot occasionally and it will "fix" the problem until the next error.