time machine error occurred during backup - but new backup disk with no first aid issues

Created at: 2021-05-14 09:08:17
Questioner General

Hello,



My time machine backups started to fail today, but with an error that is lacking in details

Time Machine couldn’t complete the backup to BACKUPDISK
An error occurred while preparing the backup.

I'm running Big Sur on an 8-core iMac. My 8TB USB3 backup disk is new, just a couple of weeks old, and has been working fine w/ Time Machine since I got it. I ran first aid on the backup disk in case it is faulty, and the tests passed without issues.



How can I get more details on the error to know how to fix this issue? I have heard I should try first aid on my boot disk too, in recovery mode, but have not tried that. Prefer to get more insights first...



Thanks!





Answer #1:

By: Dr. Orin Hoppe

Hello,



My time machine backups started to fail today, but with an error that is lacking in details

Time Machine couldn’t complete the backup to BACKUPDISK
An error occurred while preparing the backup.

I'm running Big Sur on an 8-core iMac. My 8TB USB3 backup disk is new, just a couple of weeks old, and has been working fine w/ Time Machine since I got it. I ran first aid on the backup disk in case it is faulty, and the tests passed without issues.



How can I get more details on the error to know how to fix this issue? I have heard I should try first aid on my boot disk too, in recovery mode, but have not tried that. Prefer to get more insights first...



Thanks!





Answer #2:

By: Melyssa Pouros

I should note - I ran first aid on all of the source disks too, including the boot disk - it passed in all cases. So I really have no idea what to fix in order to get time machine to work again. Is there any way to get details on what the error is?

Answer #3:

By: Rowena Pollich

I can say I never found the cause - not boot disk, other disks that are backed up, nor backup disk. Restarts, reboots, updates didn't work.



But then I turned off Time Machine, removed the backup disk, unmounted, remounted, then turned on time machine again and selected the same backup disk - and it worked again.



Not a very clear and fun experience. It'd be nice to have had more insights into why time machine was failing in the first place.

Answer #4:

By: Prof. Otha Wunsch

My situation is very similar. Backing up to two external drives suddenly started failing. Running TheTimeMachineMechanic shows at the end of each log:

Backup failed (303: BACKUP_FAILED_PREFLIGHT_STAGE_GATHER_EVENTS)

I have not found anything to explain this error message, but the simultaneous failures involving both external drives and the wording of the error messages implies that the failures occur before writing to the drives, thus are originating within the computer or internal drive.