Time Machine Synology NAS drive keeps disconnecting on macOS Sequoia

General
1

After upgrading my 2018 MacBook to the latest macOS 15 Sequoia, Time Machine no longer backs up to my Synology NAS drive. I 've been backing up my Mac to this folder on a Synology DS413 drive via Time Machine since 2019 and it always works. My wife’s Mini also backs up to the same NAS and runs successfully on macOS Sonoma. So I’m certain it’s something with macOS Sequoia.

Now, every time I try to back up to the NAS folder, Time Machine reports the error " Time Machine couldn’t complete the backup to “TMFolder” The network disk disconnected from your Mac while backing up. Make sure the computer and the backup disk are on the same network, and that the backup disk is turned on."

How do I fix this? P.S. My Mac and the backup disk are on the same network.

2

Have you tried to turn off the firewall? I had the same issue and solved it by disenabling the firewall. Here’s how:

  1. Open the Apple menu > System Settings.
  2. Click Network > Firewall.
  3. Toggle it off.

Not sure why macOS Sequoia doesn’t allow the firewall when backing up to a NAS with Time Machine. I had no such issues on macOS Sonoma and earlier.

3

Disable anti-virus programs on your Mac.

Those security applications can sometimes block the connection and disconnect the NAS drive.

4

Is your Synology DiskStation Manager up to date?

If there’s a new update available, consider getting it. It’s possible that your Synology software isn’t compatible with macOS Sequoia.

To update it manually:

  1. Go to the Synology Download Center.
  2. Select your product type and model.
  3. Scroll down the the middle of the page and click Operating System.
  4. Choose your current software version and the one you want to upgrade to.
  5. Download all patches.
  6. On your Synology NAS, open Control Panel > Update & Restore > Manual DSM Update.
  7. Choose the downloaded patches.
  8. Repeat the steps until all updates are installed.