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Level 1

8 points

Big Sur - Time Machine Backup Failing to External Drive

I recently replaced my iMac a the previous one finally died.

There is an external drive on the iMac that Time Machine will back up to with no problems.

I also have a Macbook that I was previously able to backup to an external drive on the iMac.

This is now failing with the Time Machine unable to authenticate to the server.

I have set up sharing on the iMac and given both specific user and guest access with read-write, enabled the drive for Time Machine backup, but continue to get the same error.

Has anyone been able to get this to work since the Big Sur upgrade

Posted on Apr 5, 2021 7:33 PM

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cahuna Author

Level 1

8 points

Posted on Apr 6, 2021 2:02 PM

Thankyou Barberlives123,

I did manage to resolve my problem. Not 100% sure what step exactly resolved it, but my Big Sur Macbook can now find & back up to the shared drive connected to my Big Sur iMac.

Firstly, I found that there were some Time Machine icons still displaying on my Macbook desktop that was from when I briefly connected the backup drive directly to my Macbook to back it up when my original iMac died. I removed these as they seemed to be confusing the Time machine backup process & it was looking for a locally connected drive.

Secondly, based on a suggestion in an article about a similar problem in Catalina days, I turned off file sharing & re-enabled on the iMac (server), and then restarted Finder on my Macbook (consumer).

Lastly, I created a new username on my iMac (server) for the Macbook, with Read/Write privileges to the shared Time Machine backup drive.

It the connected and backup was able to resume, appending to the original backup files.

The fact that I had replaced my iMac & restored it from a Time Machine backup seemed to be causing underlying security issues for the previous username at login to remote system & accessing the drive.

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Big Sur - Time Machine Backup Failing to External Drive

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