Connection Drops with SMB Servers on macOS Sequoia 15.1

I had these same issues. My shares mounted in macOS with no issue however, during file transfer, it would kill my whole network stack. I am talking the transfer would stall after 20 seconds to 2 minutes, then the entire network services on macOS would failover, then NAS share disconnects and transfer failed.

My setup was mounting to some Synology NAS shares (DSM 6 and 7), TrueNAS shares, and just regular old linux box shares.

All other client (non macOS) were rock solid, either via SMB or NFS. macOS clients, absolute garbage with SMB.

I tried all sorts of suggestions and configurations to /etc/nsmb.conf. I tried all manner of permissions and service configurations with DSM and exports. These SMB transfer fails are HEROIC failures with macOS.

What has finally worked for me is the absolute DUMBEST fix for an issue I have come across in my 23+ years of user/admin of such environments.

When authenticating to mount the shares, change one character of your user name to be a CAPITAL letter. For example, if you normally mount with a user name of:

nasuser1

Change the user name to be:

Nasuser1

As far as I can tell, adding a capital to any character in your user name has the same effect.

This 100% fixed my file transfer problems on macOS SMB mounts. All clients.

I do not know if this is an artifact of keychain drift over time, some odd formatting of saved credentials, whatever.

Just in case, I am pasting my nsmb.conf content here if it is useful to anyone. A few things are specific to my environment like forcing SMB 3 and disabling signing (I only mount SMB on shares I own in my own network so I am relatively confident in the authenticity). I absolutely HATE the idea of globally disabling such a security feature as packet signing, but alas, Apple has foisted this on us with poor implements of SMB...but I digress.

nsmb.conf

#Try and use NTFS stream if able
streams=yes

#Soft mount so the system don't flip itself off in a fail
soft=yes

#Remove packet signing because Apple does Apple things with established protocols
signing_required=no

#Disable directory cache
dir_cache_max_cnt=0
dir_cache_max=0
dir_cache_off=yes

#SMB3 Only, change value to 6 if need to support 2 and 3.
protocol_vers_map=4

#Remove other SMB1 features because we do not use SMB1
port445=no_netbios
validate_neg_off=yes

#Do not notify
notify_off=yes

#Do the multichannel if avail
mc_on=yes
mc_prefer_wired=yes

So, in conclusion:

I tried all the nsmb.conf optimizations I came across in hundreds of forum posts. They definitely improved the overall transfer speed when transfers were running, but the connection drops that killed my whole networking services on client were ultimately fixed by adding a capital letter in my username when authenticating.

No clue as to why, but for those that have tried everything else, what have you to lose?

Thanks, just checked and my username is Darrell with a capital D.

Looks like my /etc/nsmb.conf only contains:

[default]
signing_required=no

Will try the options you listed to see if the solution requires a capital letter plus something else in your nsmb.conf

Nope, my user name already has a capital letter in it. Perhaps something to do with attaching using a different username?

Same issue with 15.2 as well. SMB drops, but network appea4rs stable. I had a persistent ping going to the NAS (Synology) waiting for SMB to drop, and when it did, not packet loss.

It is easy to solve it: Just create the file /etc/nfs.conf with the following configuration:

nfs.client.mount.options = nfc

Reboot your Mac, end you will see the special characters without issues.

So I guess you can't edit posts here.

I tried all the nsmb.conf recomendations, usernames with a capital letter, praying to the sun god, etc., but switching from SMB to AFP, and my large file editing flow has been flawless for over 12 hours of continuous operation. On SMB it'd be having issues nearly hourly. I"m using Tdarr to convert viaeo stored on the Synology, so each file is 1-3GB in size. What I noticed is that the SMB connection was dying/getting flakey when tryign to write to the NAS. Synology supposedly fixed that specific bug in a recent SMB package update, but I'm dubious.

I'll share this on their community as well, since I'm sure my NAS is going to nag me about this AFP bit every time I log in, now.

Sequoia 15.2 on a 2024 Mac Mini M4 Pro

Synology DS923+ running DSM 7.2.2-72806 with SMB package version 4.15.13-2321

Of course now DSM is yelling at me about using AFP instead of SMB. I would rather have stability than janky SMB connectivity.

I have had multiple problems using SMB with Macos Sequoia 15, and 15.1 and Synology DSM 7.2.2 (but happened on other 7.x versions also). Moving a single file was ok, but if I start multiple copy operations Finder would freeze completely, and become totally unresponsive, and the copy operation would hang. I tried all manner of fixes and changes to the SMB configuration, but nothing worked or made any difference. Eventually I gave up and switched SMB off and used NFS. It has been flawless with zero errors and supports multiple concurrent operations without any issues. My only complaint is that file deletes over NFS are very slow, but I don't do that often so thats not an issue for me.

For anyone having this issue, this fixed it for me.

Force SMBv3

For Signing

For Synology users, you can do both of these Control Panel > File Services > SMB > Advanced Settings.

In addition to that, you may want to force this in /etc/nsmb.conf on the Mac clients, as others have posted about.

[default]

streams=yes

soft=yes

signing_required=yes

dir_cache_off=no

protocol_vers_map=6

port445=no_netbios

notify_off=yes

mc_prefer_wired=yes

****, thats whacky. Best I could tell my remaining issues once I had a proper conf in place for smb were owing to some stale keychain/passwords/whatever entries I had. The capital letter was just my form of forcing these entries to refresh themselves I guess. Even deleting the entries outright didn't fix it. But once I swapped in the capital letter on username and re-did all of my saved passwords for the shares, it kicked it into gear.

It may be complete coincidence, however. What I can say is bare bones, what seemed to get this working on all my clients was the conf I put above for my use, and forcing all my keychain/passwords saved credentials to refresh for the SMB shares (via deletion, capital letter, resaving the credentials).

Clearly YMMV, but at the end of the day we really need Apple to give us proper SMB if they are going to have SMB. My folks don't buy Mac hardware to futz this deep into protocol configs.

Good luck folks