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Big Sur and SMB Issues

I upgraded to Big Sur and now have found a weird issue with my SMB connection for work. I can connect just fine, but as soon as I try and save anything to the server, the connection drops and completely breaks my network connection. Wipes out Email, chat and internet functions but still shows I'm connected to wifi or ethernet.


We've tried other SMB troubleshooting and nothing has worked yet.

Posted on Dec 15, 2020 8:24 AM

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21 replies

Apr 22, 2021 9:47 AM in response to Brooke_22

I am having the same issue. Connecting to a remote server via SMB over a VPN. We get disconnected from the server (But not the VPN). When transferring files or opening files after about 5-8 minutes of using the server we get disconnected from the server itself. I can see this in real-time because I have a Terminal window pinging the IP of the server and I can see when it gets disconnected. I found this article which did seem to help. https://support.apple.com/en-us/HT208209. However, after a day of working very well, the problem persists.


I have 2 brand new iMac Pro's we literally purchased this year that are both experiencing the same exact issue. This is ironic because only the iMac Pro's are the only machines having the issue. We have Mac Mini M1's and Mac Pro Towers that work perfectly fine.


Considering we live in a mostly remote society today to earn a living it's critical we have a stable Server connection. Since most business servers are typically windows based SMB is crucial.


Please help Apple.

Dec 21, 2020 3:11 PM in response to helenbrk

That's interesting. I have no VPN installed, so I only access the NAS when not using VPN. I can download files > 200GB, but trying to upload something as small as 5MB to the NAS messes up all networking. I have to reboot to reset networking to even use Chrome. Not like I have old hardware either, I'm using a 16" 2019 Macbook Pro with an i9 and 16GB RAM.

May 6, 2021 10:19 AM in response to humpb

We're seeing a similar issue with our network. We've got several different SMB servers, including an older Isilon, Windows server, and Liiix-based NASs. If you're on our local network, all will mount just fine. HOWEVER, if you're on the VPN (Palo Alto GlobalProtect), you can't mount from the Isilon. Fails at the auth.


We've looked hard at the firewall logs, but there's nothing apparent. It's really odd that only that one type of SMB mount fails, and only over the VPN. It is SMB v1, but if that were the issue, then it wouldn't mount locally either.



May 18, 2021 8:41 PM in response to Mitch Roz 3

May 17, 2021

OMG! This thread is the closest I've seen to a Mac-SMB problem I've had in various forms for years. I've torn my hair out and cursed Apple countless times for pathetic SMB service and no official tutorials that I've seen on how to deal with its implementation of Samba and the innumerable tweaks it has introduced.

The latest version: M1 MacBookAir 2020, Macos 11.2.3. SMB served up from Synology 716+ (latest DSM [6.2..?].). No VPN here. First problem: transfers pathetically slow, though slightly better after implementing a couple of the common "how-tos" posted around (e.g. no signing, vfs:fruit on the server, ...) - it's like an old 56k modem. Biggest problem: with files from the server open, suddenly the machine seems to lose track of them, tell me it doesn't know where they are, that I don't have permissions for them, and I'll need to duplicate the local files and resave back to the server. This is no way for a megabillion dollar computer company to provide network capabilities. My old OS/2 box did better. My OpenSuse computer is flawless and greased lightning connecting to the Synology.

Might there be some problem introduced by the new file structure Apple has created?? Automounts appear to work fine once the maps are changed for the new mount point (/System/Volumes/Data/...). But they seem to be less than robust.

Sorry for the rant... first chance I've had to let off steam. In short, SMB is *very* frustrating on Mac, even M1.

May 25, 2021 9:58 AM in response to melstrom

May 25, 2021

Having posted this particular rant, I see it as only fair to report back on some success. In an effort to find some remedy to the slow, unstable SMB on my M1 Macbook Air, I had followed the extensive testing by one user (rolande.wordpress.com) to modify a number of TCP system settings via sysctl. In particular, for High Sierra and Mojave, the suggestion was to use the following values (NB: these seemed *not* to help, perhaps make things worse):

net.inet.tcp.mssdflt=1448

net.inet.tcp.blackhole=2

net.inet.tcp.slowstart_flightsize=60

net.inet.tcp.sendspace=3125000

net.inet.tcp.recvspace=3125000

net.inet.tcp.win_scale_factor=6

net.inet.tcp.autorcvbufmax=3125000

net.inet.tcp.autosndbufmax=3125000

By chance I neglected to run the script setting these values shortly after my original posting, leaving the default values set. Since then, my SMB connections have been very stable with tolerable speed. It is slower than my OpenSuSE machine, but it is not disruptive.

What *did* make a difference, with the Synology, at least, was the server and client settings suggested at this article (https://tinyurl.com/2rwh257h) at tech.setepontos.com, especially the vfs:fruit module on the server.

Jun 14, 2021 10:48 AM in response to Brooke_22

Similar issue here over Cisco AnyConnect VPN. Just upgraded to version 4.10.01075 and the problem persists. Connecting SMB to two IP addresses at work, a Windows server and my iMac in the office, produces difference results. The Windows server connection drops after 3-5 minutes whether there's activity (copying files, etc.) or not. However, the iMac connection stays connected just fine. The VPN connection stays stable through it all.


Thoughts? Does this behavior – Windows server connection drops while iMac connection doesn't – give anybody any ideas? I'm stumped.

Big Sur and SMB Issues

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