I have found that enabling jumbo frames on TrueNAS SCALE 24.04.2.5 and 24.10.1 severely impacts file transfer performance using SMB. Both the server and client utilise 10Gb network interfaces and NVMe storage, and iperf suggests no issues with throughput:
Additionally, there appears to be no problem with fragmentation:
TrueNAS is running on VMware ESXi 8.0.3 with 4 CPU cores, 16GB memory and a VMXNET3 network interface. All virtual machines on the hypervisor use jumbo frames without any problems with the exception of TrueNAS SCALE.
The specific workload I have been having a problem with is a scheduled sync task on the client, in which around 750GB of data comprised of approximately 400k files is compared for changes with those on the server over SMB. When the server MTU is 1500, this task completes in exactly 10 seconds. When the server MTU is 9000, this task rarely completes, experiencing timeouts, disconnects, and the SMB share becomes completely unresponsive for several minutes.
Try as I might, I have not been able to determine exactly why this is happening. The server does not appear to be under any noticeable load and I have not been able to identify meaningful error messages. I would really appreciate some help please!