Disk utility first aid fails for external hard drive used for time machine back ups, but runs fine in safe and recovery mode

Hello DoubleW,

Thanks for reaching out to Apple Support Communities. We see you have some questions about running First Aid on your external hard drive, and we'd like to help. The following link may be able to assist as it can walk through repairing a storage device on your Mac: Repair a storage device in Disk Utility on Mac - Apple Support

1) In the Disk Utility app  on your Mac, choose View > Show All Devices.

If Disk Utility isn’t open, click the Launchpad icon  in the Dock, type Disk Utility in the Search field, then click the Disk Utility icon .

Note: If you’re checking your startup disk or startup volume, restart your computer in macOS Recovery, select Disk Utility in the macOS Recovery window, then click Continue. If you check your startup volume (Macintosh HD), make sure you also check your data volume (Macintosh HD - Data).

2) In the sidebar, select a volume, then click the First Aid button .

3) In the First Aid dialog, click Run, then follow the onscreen instructions.

4) When the First Aid process is complete, click Done.

5) Repeat steps 2 through 4 for each volume on the storage device.

6) In the sidebar, select a container, then click the First Aid button .

7) In the First Aid dialog, click Run, then follow the onscreen instructions.

8) When the First Aid process is complete, click Done.

9) Repeat steps 6 through 8 for each container on the storage device.

10) In the sidebar, select the storage device, then click the First Aid button .

11) In the First Aid dialog, click Run, then follow the onscreen instructions.

12) When the First Aid process is complete, click Done.

If you still need help, please reach out to Apple Support, to look into this further: Contact - Official Apple Support

Regards.

DoubleW wrote:

Just like the title says, I have a LaCie 2TB external hard drive for time machine backups. The first aid function in disk utility fails for this hard drive normally, but it works fine in safe and recovery mode.

But could be the problem?

This is the error message I get.

https://discussions.apple.com/content/attachment/77ab928f-2322-479e-99f0-316592864dd9

It looks like something is mounting the drive during the First Aid when not in safe mode. That will always cause an error. Safe Mode apparently disables something (software) that interferes with Disk Utility First or mounts the drive when it shouldn't. Hence Disk Utility First Aid is working in Safe Mode.

Try turning off Time Machine backups and then run Disk Utility First Aid. I doubt this is the answer, I have run First Aid on Time Machine volumes without turning off Time Machine.

How is the external drive formatted (it should be GUID APFS)? How is it connected to the Mac? DO you have any LaCie utilities or disk tools installed? Do you have any anti-virus or security or cleaning utilities installed? Other disk-related software tools of any sort?

It might help diagnosis of what the conflicting software is by downloading and running Etrecheck, allow it full disk access, and posting the output here using the Additional text button below. I think there is something installed that conflicts with Disk Utility, which is not a good state of affairs and should be fixed as soon as possible, because Disk Utility has other important functions that you want to work properly when you need them.