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Sequoia Time Machine Synology NAS keeps disconnecting

I have just upgraded my 2018 Mac Mini to MacOS 15 Sequoia.

Since 2019 it has always backed up to a folder called TMFolder on a Synology DS413j.

( My partner's Mini also backs up to the same NAS, but hers is still on Sonoma. Her backups still run successfully. )


Every time Time Machine on my Mini tries to backup to the NAS now, it reports:

The backup will fail anywhere between one and five minutes after starting.


Mac mini, macOS 15.0

Posted on Sep 18, 2024 12:06 AM

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Question marked as Top-ranking reply

Posted on Oct 5, 2024 11:57 AM

In my case I had updated to 15.0.1 and then experienced the problem. Turning the macOS firewall OFF was the only way I've found to complete a backup to my Synology NAS. Previously I was able to back up with the firewall on while on Sequoia 15.0.

101 replies

Oct 30, 2024 12:41 AM in response to Blazejos

I upgraded my macbookair M2 to 15.1. It is not helping. I get the error "time machine did not finish backing up because some files were unavailable. Backups will resume when your mac is unlocked".

I am convinced there are two issues affectingTM backups: the first, linked to firewall etc. which appears to be solved by 15.1, the second has something to do with "sleep" or inactivity control. If the mac goes to sleep or is inactive during backup, the error shows up. No way out...

Sep 18, 2024 6:42 PM in response to macquarius

When will Apple crushes this bug finally? In version 20? Djeezzz.

It’s not an Apple bug. It is a Synology bug.


Prior to their SMB 3 implementation, they use Netatalk which is a hack of Apple Filing Protocol (AFP). Apple has never licensed AFP. When Apple switched to SMB networking, they set a specification for Time Machine over SMB. It is up to Synology to support that specification.

Sep 22, 2024 8:09 AM in response to spoona

I am running the final release of macOS 15 and fixed the issue by going to Apple > System Settings > Privacy & Security > Full Disk Access > toggle ON smbd. It seems macOS 15 disables the 'smbd' by default. The 'smbd' option provides filesharing and printing services using the SMB protocol which is what Synology is using to broadcast its file and folder shares.

Sep 23, 2024 4:58 AM in response to Mike Richards2

Thank you for posting your experience. so you essentially re-did the macOS<>synology time machine integration and it's still not working the same as it was prior to the update from sonoma to sequoia? new folder, proper time machine folder settings, create the new time machine backup, etc... you did all that and it's still not working? ughhhhh


For me, that's always been the workaround that i've found solves these problems after a new macOS update. When macOS updates, can't think of a year that I wasn't forced to completely reintegrate time machine with my synology. it's always awful every year, but at least it still works in the end... not this time tho?

Sep 23, 2024 6:40 AM in response to kmrkev

'Fraid so.


I've chatted with Apple twice now.


The first time they asked me to try and start the iMac Pro in Safe Mode (failed with same error); to create a new account (failed); and reinstalling Sequoia (initially seemed to work, but then it failed overnight with the same error and has failed every time since).


I've chatted with them again and I'm waiting for a call back. First line support is saying they've not heard of this error before, so I have pointed them to this thread.


My MBA is updating completely reliably throughout.


I'll keep people informed.

Sep 27, 2024 6:13 AM in response to spoona

I am afraid the problem is on Apple's side.

I have a Synology DS218+ at home, and I have this issue with my MacBook Air recently updated to Sequoia.

I back up the same MacBook Air at work on a Western Digital My Cloud NAS, and I have precisely the same problem.

I have the impression it is triggered when I leave the computer unattended (inactivity? Sleep?), even if in the Battery panel I have ON the switch "Prevent automatic sleeping on power adapter when the display is off".

I tried only once an overnight backup on an external SSD, and next morning I found the red dot with the "i" in the Time Machine control panel and the message "backup could not complete because some files are not available...etc."

Hope they fix it in 15.0.1/15.1.

Oct 16, 2024 4:41 AM in response to spoona

Yes, that worked for me too, for a while and then it suddenly stopped working again. I saw a post here (that I now can't find) that suggested re-starting in safe mode and then re-starting normally. I did that and, with the firewall off, my backups are working again. Not sure quite what that did, but certainly did the trick for me.

Sequoia Time Machine Synology NAS keeps disconnecting

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