[SOLVED!] Very slow file transfer on Mac Shares (SMB/AFP)

Once I implemented this fix I went from getting 10MB/s to getting over 500MB/s+ (both read & write) on my Mac laptop connected over Wifi.

BEFORE/AFTER:

 

 

 

 

 

 

On MacOS 10.13.x I was getting terrible network transfer speeds from my Mac laptop to the network share being served by another mac. We were only getting 10MB/s which was not even enough to stream videos at 720p but yet on the iMac this external RAID array was attached to we were getting 200MB/s+ and could stream 2160p30 (4k) videos no problem.

Server serving the network share:
MacOS High Sierra (10.13.6), External 24TB RAID array in RAID 10.

Client access the network share (SLOW):
MacOS High Sierra 10.13.4 (also happens in 10.13.5)

The fix:

Make the change temporary (without rebooting):

1. Open a terminal
   
2. sudo sysctl -w net.inet.tcp.delayed_ack=0

   1	sudo sysctl -w net.inet.tcp.delayed_ack=0

3. Close and re-open Finder and see if the problem goes away. Also close and re-open your throughput testing app (in my case BlackMagic Disk Speed Test app) before testing again (required!). This setting for me was set to 3, changing it to 0 fixed it and then changing back to 3 caused it to drop back down to 10MB/s, confirming the resolution.

To make the change permanent (requires reboot):

1. Create/edit the file /etc/sysctl.conf
2. sudo vim /etc/sysctl.conf

   1	sudo vim /etc/sysctl.conf

3. Add this line to the configuration file:
4. net.inet.tcp.delayed_ack=0

   1	net.inet.tcp.delayed_ack=0

5. Save and close file (type “:wq” without quotes, then hit enter)
   reboot computer
   Open finder and your problem should be resolved.
6. If it is not, try the guide that shows how to enable vfs_fruit module for Samba, I believe this is only useful if the server hosting the share is NOT a Mac as it enables better Mac compatibility for Samba. You can also try installing Samba instead of the MacOS implementation of SMB.

The Mac laptop that was struggling I had tried multiple known fixes before this:

1. Disabling SMB Signing (smb_signing) and it did show it as disabled in the terminal but had no impact for me. I disabled on both server and client and reconnected the share and restarted all services.
2. Changing connection from SMB to AFP, reconnected share, no impact
3. The final change, disabling Delayed TCP ack, fixed it.