TerraMaster Forum

I created a new share for Time Machine backups (TimeMachineBackups)and added this to the Backup->Time Machine list of Authorised Directories. I also created a new user "tm-user" with read/write access to the Time Machine share and was able to configure this as a destination target in the macOS Time Machine settings.

However, a few seconds are starting, the backup errors out with this following message:

"Time Machine couldn’t complete the backup to “TimeMachineBackups”
The backup disk image could not be created.

I can see that some files are created in the share under a new folder with a GUID-like name each time a backup is attempted, e.g.

9A39CA87-XXXX-XXX-XXX-XXXX.purgable
token
> mapped
lock
info.plist

This folder is owned by the "tm-user", but clearly this user seems to be unable to carry out the actual backup. tm-user has read/write permissions, and I've also tried applying the folder permissions to all subdirectories.

Any idea what is going on?

Do TM backups only work in the public folder? If so, why is this folder any different to other shared folders?

Thanks

We are trying to verify the problem.
Could you please provide us with the TOS version number and macOS version number? This will help us to better troubleshoot the issue.

TMzethar wrote: ↑17 Jun 2024, 18:50 We are trying to verify the problem.
Could you please provide us with the TOS version number and macOS version number? This will help us to better troubleshoot the issue.

Thanks. I'm using macOS 14.5 (latest update @18 June 24) and TOS 5.1.131-00123 on a new F4-424 NAS

I have enabled the SMB file service but disabled AFP.

I have had some issues with macOS somehow "caching" the "wrong" NAS user credentials. e.g. if I set up Time Machine to use a NAS user "tm-user", and then try to access a NAS share via the Finder, sometimes I see that the credentials for accessing the share have reverted from my usual NAS user (either the admin user or another user with read/write permissions to the share) to the "tm-user", even though the NAS volume was never directly accessed from the Finder using this user. It is as if macOS "remembers" a recently used "tm-user" to run a Time Machine backup and then assumes I want to use the same NAS user account to access other shares. This generally means the Finder fails to open shared folders (or sub-folders within the shares) due to permission errors (i.e.the "tm-user" can't access my "video" share because it intentionally doesn't have permission to do so).

As you said, this should be the cause of the problem.
TimeMachine backup relies on existing SMB credentials, and on a MAC/PC terminal, only one SMB credential can exist for the same target server (NAS).

TMzethar wrote: ↑20 Jun 2024, 13:51 and on a MAC/PC terminal, only one SMB credential can exist for the same target server (NAS).

Can this be clarified? - One SMB credential per user on any given MAC/PC terminal

Yes, in some cases, PC/MAC devices may have multiple users, and each user can have different SMB credential configurations.

TMzethar wrote: ↑20 Jun 2024, 19:20 Yes, in some cases, PC/MAC devices may have multiple users, and each user can have different SMB credential configurations.

Just to clarify, are you saying any given macOS user, e.g. "macuser" may only be able to the connect to *any* share on the NAS with only a *single* NAS user account at one time? This seems to be extremely limiting if you have multiple NAS user accounts for different purposes. For example, I want to have the following shared NAS folders:

TimeMachineBackups
NASVideo
NASMusic

...and ideally want 3 different NAS user accounts:

"tm-user" -> has read/write access to TimeMachineBackups - other users "denied" access
"editor" -> has read/write access to NASVideo - other users "denied" access
"plex" - has read/write access to NASMusic - other users "denied" access

I want to access these shares from the macOS Finder, after mounting them as:

smb://tm-user@<my NAS IP>/TimeMachineBackups
smb://editor@<my NAS IP>/NASVideo
smb://plex@<my NAS IP>/NASMusic

I've set up TimeMachine on my Mac to connect to the share with the "tm-user" and it seems to work - but *NOT* with my user-created share "TimeMachineBackups", even though this is included in the NAS TimeMachine configuration as a destination path. It only works if I create the backup on the default "public" share on the NAS.

If connect to the shares using the format above "smb://<user>@<my NAS IP>/<share name>" - it generally seems to work and remember the user credentials used to access the share, but if I don't "connect to server" with a specific user, then I can get the problem with the "wrong" user being selected to access a share, e.g. "tm-user" might show as the credentials used to connect to NAS, even though I have mounted the "NASMusic" share.

Anyway....I can probably get the behaviour I want if I always mount the share with an explicit user with the smb:// format above.

This doesn't explain why I can't make Time Machine backups to a user-defined shared folder though!

In Time Machine, when you add a backup disk, you can enter different user credentials for the backup based on the shared folder you choose.
When you want to use different users to access the same TNAS at the same time in Finder, you can plug in an extra network cable and use different users to access different IP addresses.
By the way, have you used a guest user before?