One thing that I discovered the other day :
smbd spins 100% CPU when data is being copied to Windows client (~450-500mb/s)
but if I copy from a Linux client it hovers around 30-40% and I get 1.15gb/s speed
I initially thought this could be something to do with SMB encryption, but it is explicitly disabled in TrueNAS cli
[nas]> service smb update smb_options="use sendfile = yes\naio read size = 1\naio write size = 1\ninterfaces=\"192.168.1.3;speed=25000000000,capability=RSS\"\nserver smb encrypt = off"
[nas]> service smb config
+-------------------+-----------------------------------------------------------+
| smb_options | use sendfile = yes |
| | aio read size = 1 |
| | aio write size = 1 |
| | interfaces="192.168.1.3;speed=25000000000,capability=RSS" |
| | server smb encrypt = off |
| bindip | 192.168.1.3 |
+-------------------+-----------------------------------------------------------+