I have no explanation or even speculation as to why that was happening. For example, I noted that when my backups failed I would have two (2) users that had privileges to that shared folder attempt to connect nearly simultaneously from the same Mac even though I had only supplied one user credentials when selecting the share in Time Machine setup. Check if when a Time Machine backup initiates whether you have more than one user attempting the connection.

After rebooting a Mac I then selected the new destination on on my Synology device using the credentials of the sole user with those permissions.īut before doing any of that take a look at the Connections log on your DSM (DSM>Main Menu>Log Center, and select Connections from the drop down menu.I then shutdown each Mac and did an SMC reset (not NVRAM).On my Macs I removed the existing Time Machine destination and unchecked automatic backup.On my Macs I also uninstalled the Sophos AV as well.On my Big Sur Macs I totally stopped the Spotlight Indexing Service altogether (in Terminal: sudo mdutil -i off).In DSM>Control Panel>Users I went through each user to ensure none other than the one (1) I had selected for Time Machine backups had permissions to that shared folder, and I ensured that user had an unlimited quota.In DSM>Shared Folder>Permissions I ensured that only one (1) of the users I created had privileges to the newly created Time Machine folder.I went back to DSM>Control Panel>File Services>Advanced Settings>Set Time Machine Folders and picked the new one I just created. In DSM I deleted the existing shared folder that I designated for Time Machine and created a new one.In DSM>Control Panel>File Services>Advanced I ensured that Bonjour discovery was enabled for both SMB & AFP. I kept AFP enabled even though it has been deprecated in Big Sur. In DSM>Control Panel>File Services>SMB/AFP/NFS select SMB Advanced Settings and set maximum SMB Protocol to SMB3 and minimum to SMB1.Here's what I did overall to get it working and it is now working on all my Big Sur implementations (4):

Best way to backup mac to synology