TimeMachine Big Sur to Synology NAS

Sophos Home blocked TimeMachine on a NAS and removing it worked for me.

I have now installed Bit defender instead as an anti virus checker and everything including TimeMachine is still working normally on the NAS.

As far as Big Sur is concerned, everybody needs to forget AFP as it has been deprecated. Also, everybody needs to get off the concern regarding APFS with respect to network backups - as those drives are not formatted in APFS. The issue is third party antivirus/malware protection, and in particular, at least in my case, Sophos. Sophos has documented that it breaks Time Machine network backups, and still has inexplicably failed to fix it. In about 20 seconds I'm going to dump them forever.

I was able to get it working by following the steps in this article: https://www.synology.com/en-us/knowledgebase/DSM/tutorial/Backup/What_should_I_do_to_fix_the_problem_when_connecting_to_Synology_NAS_using_Time_Machine

I have one user with access to the shared Time Machine Folder on the NAS. I have only SMB enabled and left the advanced settings for SMB as default.

TM is backing up now, keeping my fingers crossed that this is not a recurring issue.

Success! Removing Sophos Home as per instructions by Bear Down worked for me too after Time Machine on Synology failed since upgrading to Big Sur. Not sure what to do now re AV protection.

Yes, Sophos Home installed on Big Sur blocks Time Machine from backing up to ANY network device, not just Synology. Broken for Western Digital, Seagate, Netgear, Buffalo - you name it.

We like Sophos, but as we have learned it breaks Time Machine on Big Sur. Not even sure Sophos is aware as their latest support document re: Big Sur makes no mention, just all the Sophos AV features that DO NOT work on Big Sur and the system gymnastics necessary to get it to even install and minimally function.

Most NAS devices use either AFP or SMB. My NAS sets up any share for Time Machine as AFP, so yes, this impacts my backups. I found that Sophos Home was blocking how Time Machine wanted to use the AFP share.

I haven't seen any specific mention of AVG causing the same problem, but I would bet that *any* third-party anti-virus software on Big Sur blocks Time Machine. It would be worth a try to uninstall AVG, reboot, then try Time Machine again.

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.

This isn't specific to Synology NAS devices. I just replaced a WD My Cloud EX2 Ultra with a Synology DS218+ because of this issue and Big Sur Time Machine fails on both. Both work when running Catalina Time Machine. Pretty sure this is a Big Sur issue. I am considering abandoning Big Sur and going back to Catalina at this point.

AFP has been deprecated in Big Sur.

My NAS is Allison on this version. I updated my Mac Mini (final Intel version) yesterday. I also checked too ensure the NAS was only using SMB 2/3 (although it unhelpfully describes the connection as CIFS). I use the same account for time machine as I do to access the NAS. Backup ran smoothly and continues to do so. Not sure if this was due to the .1 release of MACOS or release 3 from Synology, but all appears to be well!

it Sophos that causing the problem. Removing it resolve the issue for me.

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.