Hi everyone,

I’m having a persistent issue with Time Machine on macOS (Tahoe) with my Synology NAS, and Id like to know if anyone else has experienced this or found a reliable fix.

Problem:

Time Machine keeps doing full backups every time instead of incremental ones.

The first full backup is expected, but several hours later when TM runs again, it starts another complete backup from scratch (hundreds of GB), as if the previous backup didn’t exist.

1To+ in one day !

My setup:

• MacBook Pro (APFS internal disk)

• Synology NAS using SMB for Time Machine

• Dedicated user created for TM

• Shared folder “Time Machine Backup”

• SMB settings on macOS customized via nsmb.conf

• TM sparsebundle freshly created

• No encryption issues

• No network drops

• TM mounts the NAS correctly under .timemachine/

What I observed:

• The sparsebundle mounts as a disk image (disk4) containing an APFS container (disk5) and a volume named “Sauvegardes de MacBook Pro de xxxx” — this is normal behavior for SMB TM.

• However, the Mac sometimes creates an extra mount point under /Volumes/ with the same name.

• Even after cleaning up all local APFS TM snapshots, deleting ghost mountpoints, ejecting the disk image, and recreating the sparsebundle, Time Machine still performs a complete backup instead of incrementals.

• tmutil status always shows a full-size totalBytes, matching the entire disk (~350GB+).

What I’ve already tried:

• Deleted all local Time Machine snapshots (diskutil apfs deleteSnapshot)

• Removed stale mount points from /Volumes/

• Fully disabled TM via tmutil disable

• Stopped all TM processes (backupd, diskimages-helper, etc.)

• Ejected all disk images (hdiutil detach, diskutil eject)

• Deleted the sparsebundle from the NAS and recreated it

• Confirmed SMB v3 signing and streams settings

Symptoms remain:

Every time Time Machine run, even after a clean backup, it treats the next run as a new destination, resulting in another full backup.

My question:

Why is Time Machine failing to recognize the previous backup on the Synology, and forcing a full backup each time?

Is this a known bug with macOS Tahoe, Synology SMB Time Machine, or something specific to APFS/sparsebundle matching?

Any insight from people using Time Machine over SMB on Synology would be greatly appreciated.

Hey all,

I usually run Time Machine over the network with an UNRAID server.

On this beta of Tahoe at least, it doesn't seem too happy / always says an issue.

Using a local SSD works fine... but anyone else use network?

With my current macOS version 15.7.3 and the warning "Future versions of macOS might not support AFP volumes" and with my TM backup being on Synology volume, I have finally decided to search for current Synology KB for setting up TM backups and saw the following text there

"Starting from macOS Tahoe 26, Mac File Service (AFP) on SRM only supports existing Time Machine backups. As macOS 26 does not support creating new backups via AFP and SRM does not yet support SMB3, creating new Time Machine backups is not possible in this environment."

Does it mean that Synology will not be supported any more as a backup platform (at least until SMB3 support becomes available there)??

Yesterday, I noticed that my computer hasn't been backing up to my Synology NAS via Time Machine. When I try backing up, I get a message stating that the disk is not available. Another computer in the house is still backing up. Only thing different about my computer is that I'm on Apple's Beta program and am using the latest Tahoe 26.6 Beta. I also had recently updated the DSM version to the latest available but that doesn't explain why only my computer is affected.

The disk has 2.8 TB free vs my computer which only has a 1TB drive. I tried unchecking the Shared File quota and also tried setting up a new backup shared folder but get the same result.

Anyone else experiencing this or have any suggestions?