NFSv4 for Time Machine?

I've been able to identify the cause of the segfault panic. Using Samba 4.13.14-Ubuntu, enabling

server multi channel support = Yes

in your /etc/samba/smb.conf, mounting a share on a macOS client then rebooting that client causes the segfault.

This is configuration option is experimental below Samba 4.15 so not well-tested apparently. Multi-channel support is a performance enhancement in SMB3. Hopefully, this bug will be resolved soon.

BTW... found this article on optimizing Samba performance on ZFS. Curious what you think.

Re: LXD containers - makes sense.

One thing I might try is to set server multi channel support = No (or comment it out as "No" is the default until 4.15+). Could be that's related to the segfaults when clients are rebooted. Of course, this is one of the bigger benefits of SMB3 so it would be a shame to have to turn it off.

Got feedback from the Samba team that server multi channel support simply doesn't work in 4.13.x. Guess I'll have to wait for Samba 4.14 or 4.15 to make it to Ubuntu to be able to take advantage of it as I'm not motivated to build Samba from source.

Thanks a lot for the detailed response. A few follow up questions and comments...

• If you have a share mounted on a Mac running Monterey and you reboot the Mac, do you see anything odd in the Samba log on Ubuntu?
• Your /etc/avahi/services/timemachine.service matches mine. Thanks for posting this for other people in the forum to see it.
• Have you ever found setting fruit:model in the smb.conf to work? I have always had to set the icon in the Avahi service definition as you have in order to see the correct icon on macOS clients. Would have liked for this to work but it never did for me. Curious about your experience.
• Most of what's in my smb.conf are efforts to disable services not needed by macOS clients in the hope of improving performance (and stability).
• A few things I noticed about your smb.conf... fruit:advertise_fullsync = true is deprecated and was replaced with fruit:time machine = yes (https://www.samba.org/samba/docs/current/man-html/vfs_fruit.8.html). The settings fruit:aapl = Yes, ea support = Yes, durable handles = Yes, kernel oplocks = No, passdb backend = tdbsam are default values.
• Regarding posix locking = no, the docs state, "It is very unlikely that you need to set this parameter to "no", unless you are sharing from an NFS mount, which is not a good idea in the first place."
• Out of curiosity, why did you opt for isolating Samba and Avahi in a light LXD container? Was it more related to security than stability?

Here's my updated /etc/samba/smb.conf designed for Monterey macOS clients (disabling everything superfluous - alphabetized):

[global]
allow dns updates = disabled
;bind interfaces only = Yes
client min protocol = SMB3_11
dcerpc endpoint servers = rpcecho
;deadtime = 30
delete veto files = Yes
disable netbios = Yes
disable spoolss = Yes
dns forwarder = 192.168.1.1
dns proxy = No
enhanced browsing = No
# Next line requires catia (needed if no Windows clients?)
fruit:encoding = native
fruit:metadata = stream
# Next line never ever worked. Do it with Avahi instead.
;fruit:model = Macmini7
# Do not use NFS access control entries
fruit:nfs_aces = No
# Enable extended attributes (requires streams_xattr)
fruit:resource = xattr
# Next line is already the default
;fruit:zero_file_id = Yes
host msdfs = No
inherit acls = Yes
inherit permissions = Yes
;interfaces = lan
lm announce = No
load printers = No
log file = /var/log/samba/log.smbd
log level = 1
logging = file
max log size = 10000
# Next 2 lines defer mDNS config to Avahi (better for icon and Time Machine)
mdns name = mdns
multicast dns register = No
name resolve order = host bcast
pam password change = Yes
panic action = /usr/share/samba/panic-action %d
passwd chat = "*New Password:*" %n\n "*Reenter New Password:*" %n\n "*Password changed.*"
passwd program = /usr/bin/passwd %u
printcap cache time = 0
printcap name = /dev/null
printable = No
printing = bsd
restrict anonymous = 2
rpc_daemon:spoolssd = disabled
rpc_server:epmapper = disabled
rpc_server:winreg = disabled
rpc_server:lsarpc = disabled
rpc_server:samr = disabled
rpc_server:netlogon = disabled
rpc_server:netdfs = disabled
rpc_server:dssetup = disabled
rpc_server:wkssvc = disabled
rpc_server:spoolss = disabled
rpc_server:svcctl = disabled
rpc_server:ntsvcs = disabled
rpc_server:eventlog = disabled
rpc_server:initshutdown = disabled
rpc_server:mdssvc = disabled
server max protocol = SMB3_11
server min protocol = SMB3_11
# While macOS clients support the next option, client reboots will segfault Samba if uncommented
;server multi channel support = Yes
server role = standalone server
server services = rpc, smb
server string = %h server (Samba 4.13.14, Ubuntu 21.10)
show add printer wizard = No
smb ports = 445
unix password sync = Yes
use sendfile = Yes
veto files = /._*/.DS_Store/
vfs objects = catia fruit streams_xattr

[homes]
browseable = No
comment = Home Directory
fruit:time machine = No
guest ok = No
spotlight = No
valid users = %S
writable = Yes

[Backup]
comment = Time Machine
fruit:time machine = Yes
guest ok = No
path = /external/%U
spotlight = No
valid users = %U
writable = Yes

and my /etc/avahi/services/samba.service...

<?xml version="1.0" standalone='no'?>
<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
<service-group>
 <name replace-wildcards="yes">Saint James</name>
 <service>
   <type>_smb._tcp</type>
   <port>445</port>
 </service>
 <service>
   <type>_device-info._tcp</type>
   <port>0</port>
   <txt-record>model=Macmini7</txt-record>
 </service>
 <service>
   <type>_adisk._tcp</type>
   <txt-record>sys=waMa=0,adVF=0x100</txt-record>
   <txt-record>dk0=adVN=Backup,adVF=0x82</txt-record>
 </service>
</service-group>