Exfat formated USB SMB-Drive (Synolgy NAS 124) for Timemachine backup in Tahoe

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Exfat formated USB SMB-Drive (Synolgy NAS 124) for Timemachine backup in Tahoe

Is there a way to get Exfat formated USB SMB-Drive (Synolgy NAS 124) for backup to work with Timemachine in Tahoe 26.7.2?

I'm working on this since a few days and at least I got it to work with Ext4. I did all the recommended settings, but it only I only got it to work with Ext4 after all.

Trying it with exfat I got the following error when trying it to add to timemachine:

"Connection to network disk interrupted"

and in the terminal:

'/Volumes/usbshare2-2' does not support SMB FullFSync

• failed writing to [...] error: 45 Operation not supported

( after entering: After entering: log show --predicate 'subsystem == "com.apple.TimeMachine" or process == "backupd"' --info --last 10m)

So I would have saved a lot of time if I would have formatted it in Ext4 from the beginning. But my aim was to get a disk that the Mac could as well read directly, which is now not possible.

So I hope that someone got it to work with exfat.

I would appreciate very much sharing your experience. Thank You!

MacBook Air (M5, 2026)

Posted on Nov 4, 2026 10:59 AM

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Answer 1

Top-ranking reply

kaz-k

Level 9

53,696 points

Nov 4, 2026 11:23 AM in response to Alfi

Hi,

You cannot use an exFAT-formatted USB drive connected to a Synology NAS for Time Machine backups, because Time Machine requires a native file system like ext4 or Btrfs for attached USB drives on a Synology system, or an APFS structure when used locally.

Why exFAT Fails for Time Machine

File System Incompatibility: macOS and Time Machine require specific file attributes, hard links, and permission handling (POSIX/ACLs) that exFAT does not support.
Synology Limitations: When formatting external USB drives directly on a Synology NAS, Synology explicitly requires ext4 or Btrfs for Time Machine targets.
macOS Tahoe Network Quirks: macOS Tahoe introduces stricter SMB handling and capability checks. Even if shared over SMB, an underlying exFAT volume will reject sparse-bundle image creation or fail capability validation.

Recommended Solution

Reformat the USB Drive: Log into your Synology DSM, go to Control Panel > External Devices, and reformat the USB drive to Btrfs (or ext4 if Btrfs is unavailable on your specific model).
Configure via SMB Properly: Instead of sharing the raw USB mount directly via an ad-hoc exFAT structure, set up a dedicated shared folder on a healthy internal NAS volume (or properly mapped external Btrfs/ext4 drive) and enable the official "Enable Time Machine" flag in Synology's file services.
Check ASCII Naming: Ensure your computer name and network share paths do not contain special accents or non-ASCII characters, which frequently trigger permission or "disk not found" errors in Tahoe.

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Answer 2

Alfi Author

Level 1

51 points

Nov 5, 2026 2:42 AM in response to kaz-k

Yes thank you thats how I had got to work. I was hoping to Find a work around as on the Same NAS it’s working

with exfat and Time Machine but with AFP only. And with SMB with ext4 . These two TIMEMACHINE backups run from the same computer to the same NAS. And they both work.

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