On TrueNAS, Why is SMB+TimeMachine 900MB/s while Syncthing mostly runs at 166Kib/s?

Computer Hardware & Server Infrastructure Builds
1

Looking at the TrueNAS network monitor, my macOS TimeMachine backups via SMB share is a solid 900MB/s for the entire process whereas the macOS Syncthing backing up ranges from 18KiB/s sometime bursting to 100KiB/s.

Are there specific Syncthing tuning options for macOS clients or NAS hosts I might be overlooking, or is it a fundamental difference of TimeMachine “full blocks with as many files will fit” versus Syncthing serial File-at-a-time? Both NAS and macOS Syncthings are configured for direct IP connection (TCP WAN) over CAT 6E ethernet, not through a Syncthing relay.

NAS HOST: TRUENAS-MINI-3.0-X+
NAS OS: 25.04.1
NAS Syncthing 1.29.6
NAS NIC : two each 1Gbps
NAS SMB Service: “Enable SMB2/3 Durable Handles” for Apple TimeMachine access

macOS : 15.5
macOS NIC : 1Gbps ethernet to NAS HOST
macOS Syncthing 1.29.6
macOS Syncthing Shared File : Thunderbot 3 connection to 7200 RPM 6TB drive

2

Synching does have some overhead based on the encryption but is should not be that slow. How are you getting the data for the speed from the Sycnthing, via looking at the port traffic on a attached NIC? I have found there to be discrepancies, test a single large file and time it.