Samba4 and Time Machine: unable to mount volume

I’m trying to run Time Machine backups to the Turris Omnia. I’ve managed to set up Samba 4 and can access shared seemingly without issue. I managed to get a first backup to complete, but now I can’t mount the volume any longer. The Mac is giving me a very generic error message, and logread shows me this:

Sep 14 21:17:58 emerson smbd[16361]: [2021/09/14 17:17:58.894957,  0] ../../source3/modules/vfs_fruit.c:6982(fruit_tmsize_do_dirent)
Sep 14 21:17:58 emerson smbd[16361]:   fruit_tmsize_do_dirent: tmsize potential overflow: bandsize [33554432] nbands [1931]
Sep 14 21:17:58 emerson smbd[16361]: [2021/09/14 17:17:58.895241,  0] ../../source3/smbd/dfree.c:136(sys_disk_free)
Sep 14 21:17:58 emerson smbd[16361]:   sys_disk_free: VFS disk_free failed. Error was : No error information

I can mount other shares without issue. I didn’t find a lot of information about this error. Any suggestions?

[Time Machine Mary]
	path = /srv/shares/timemachine/mary
	create mask = 0666
	directory mask = 0777
	read only = no
	guest ok = no
	fruit:encoding = native
	fruit:metadata = stream
	fruit:veto_appledouble = no
	fruit:time machine = yes
	fruit:time machine max size = 350G
	vfs objects = catia fruit streams_xattr 

I need to limit the available size since I want to back up two machines to the same underlying btrfs filesystem.

maybe this will provide some hints…

… if i understand well, MacOS is trying to save some dot-files in that share, but due permissions file is not written or/and folder is not accesible …

also maybe the mask you are having should be changed (dir_mask=0775, create_mask=0664 in samba config) ; and try to lover the protocol dialect to SMB2

Cross-reference: Samba4 Time Machine: unable to mount share - Installing and Using OpenWrt - OpenWrt Forum