TimeMachine Big Sur to Synology NAS

Here's what I did overall to get it working and it is now working on all my Big Sur implementations (4):

1. In DSM>Control Panel>File Services>SMB/AFP/NFS select SMB Advanced Settings and set maximum SMB Protocol to SMB3 and minimum to SMB1. I kept AFP enabled even though it has been deprecated in Big Sur. In DSM>Control Panel>File Services>Advanced I ensured that Bonjour discovery was enabled for both SMB & AFP.
2. In DSM I deleted the existing shared folder that I designated for Time Machine and created a new one. I went back to DSM>Control Panel>File Services>Advanced Settings>Set Time Machine Folders and picked the new one I just created.
3. 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.
4. 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.
5. On my Big Sur Macs I totally stopped the Spotlight Indexing Service altogether (in Terminal: sudo mdutil -i off).
6. On my Macs I also uninstalled the Sophos AV as well.
7. On my Macs I removed the existing Time Machine destination and unchecked automatic backup.
8. I then shutdown each Mac and did an SMC reset (not NVRAM).
9. 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.

But 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. Check if when a Time Machine backup initiates whether you have more than one user attempting the connection. 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. I have no explanation or even speculation as to why that was happening.

I suspect there is a bug lurking in Big Sur regarding Apple's choice of APFS Time Machine backups that causes it to not play well with NAS devices, or in particular Synology NAS devices. It won't surprise me in the least if this is addressed in an 11.1 release. Everyone knows the 11.0.1 release was rushed to coincide with the M1 Macs show, and may not still be ready for primetime. I have a Mac I use as an Apple Music/TV/Plex server that relies on a 24tb SoftRAID RAID5 array that I cannot transition to Big Sur until SoftRAID is able to release an update (they claim their updated driver is built into the Big Sur release, but users are reporting issues and the client is beta and will be for some time). I'm just not going to risk that machine to some fatal bug that totally borks a 24tb array.

I had the very same issue after upgrading a MacBook Pro 13" to Big Sur running Sophos Home and after diving in different forums, I found the explanation on Sophos website : 

Known issues between Sophos Home and macOS 11 Big Sur - Updated December 2nd, 2020

• Since Web Protection is not yet working, expect to see a message on the Sophos Home Dashboard, stating Web Protection is disabled/device is vulnerable - You will also see that the device is vulnerable on the Sophos Home dashboard
• - Web Protection is expected to be functional with the 10.0.2 Sophos Home release - January 2021
• 
  
• Incoming SSH connections will fail if running Sophos Home v10.0.1a1 + MacOS 11 Big Sur.
• 
  
• Time Machine backups to NETWORK locations are currently failing when Sophos Home is installed on Big Sur macOS 11 - Users will see a message reading "Time Machine couldn't complete the backup - The disk is already in use" 
• This issue is currently under investigation by our development team. As a workaround, run the backup in Safe mode. 

I then started my MacBook Pro without extensions and Time Machine did its backup straight away so it is not related at all to permissions or afp or SMB, it is related to extensions barring the normal process of Time Machine. Backdraw is that you have to restart the Mac in Safe mode everytime you want to make a Time Machine backup...

For those waiting for a Sophos fix to Big Sur, looks like it will be awhile...

Known issues between Sophos Home and macOS 11 Big Sur - Updated December 2nd, 2020

• Time Machine backups to NETWORK locations are currently failing when Sophos Home is installed on Big Sur macOS 11 - Users will see a message reading "Time Machine couldn't complete the backup - The disk is already in use"  This issue is currently under investigation by our development team. As a workaround, run the backup in Safe mode. We expect this issue to be resolved by March of 2021.

Separately, re: the AFP & SMB protocols. A couple of times my Time Machine bundle got corrupted. I've found out the hard way that SMB is much more stable than AFP. While AFP may still work on earlier MAC OS, do yourself a favor and switch to SMB.

That has got to be complete bunk! Without Sophos AV I'm Time Machining 4 Big Sur machines to my Synology RAID NAS without issue. Did Apple just chuck all their Airport Time Capsules out the window? Of course not, and their 11/12/2020 notes 3 of the 4 options for backup as being SMB remote to the subject machine (https://support.apple.com/en-us/HT201250). That "senior" support rep is just someone who doesn't know what they're talking about.

There are exploits to Mac OS if you're not careful enough to avoid opening links in phishing emails or download files from unknown sources. This article is of the opinion that you don't need to pay a third party vendor for added security if you take normal precautions.

https://discussions.apple.com/docs/DOC-8841

Apple is serious about security. This page states that anti-virus is "built in" to macOS Big Sur:

https://www.apple.com/uk/macos/security/

This is from the latest Big Sur support page on Sophos:

• Time Machine backups to NETWORK locations are currently failing when Sophos Home is installed on Big Sur macOS 11 - This issue is currently under investigation by our development team. 

As of Nov 25, Sophos added the problem to their known issues:

• Time Machine backups to NETWORK locations are currently failing when Sophos Home is installed on Big Sur macOS 11 - This issue is currently under investigation by our development team. 

Bitdefender AV for Mac works fine on my four MacBooks. Used it from Mavericks up to Big Sur. No hiccups with TM backups to Synology, ever. Currently there's a 30 day free trial, see attached. There's also a free, bare-bones version in the App Store.

If you have the latest version of the Synology's DiskStation Management (DSM) software installed, and rebooted the Synology, then you need to visit Synology support to see if there are initial issues with Big Sur compatibility. Though I am not using my Synology for Time Machine backups, my older DSM 5 software still allows me to mount shares to Big Sur, and access that content in the Finder without any changes to the Synology or Big Sur settings.

Hi,

I have the same issue. Only upgraded one Mac Mini, backing up to DS218J worked fine on Catalina but now does not work under Big Sur. I can mount all my shares manually from Finder and all work fine. Must be a issue with TimeMachine. My other Macs under Catalina are backing up fine to their respective shares.

I am using the current release and updates of DSM.

Regards

Phil

Hi

I have a DS415play(latest DSM), with a TM using AFP and its all working ok for me, doesn't help you but after my upgrade this was the only thing that I didn't have to worry about, printing and weird colour inversions everywhere yes but Time Machine ...no

TM backup/restore working fine with my 2019 MBPs (macOS 11.0.1) to DS718+ (ext4 format). Changes I made in DSM: <Control Panel><Shared Folders> make a new folder, then <File Services> <Advanced> <Set Time Machine Folders>. When Time Machine is initiated, choose the newly created shared folder <Select Disk> as the backup target. Interesting to note Apple changed the TM backup file name extension from backupbundle (Catalina) to sparsebundle (Big Sur).

Up to macOS 10.14.x (Mojave) TM backups were saved as sparsebundle. With macOS 10.15.x (Catalina) TM backups were saved as a backupbundle. There were many complaints that under macOS 10.15.x (Catalina), previous TM backups saved as sparsebundle were not accessible.

Now with macOS 11.0.1 (Big Sur) TM backups are saved (again) as sparsebundle. Perhaps it follows that a sparsebundle created with Big Sur is not compatible with a backup created in Catalina as a backupbundle.

It has nothing to do with previous backups in Catalina as I have started with an empty NAS share and Big Sur won’t even start the new backup sequence. A directory is created on the share and then immediately gets deleted when the backup stalls after 10s of seconds.