Do not configure multiple SMB multichannel interfaces on the same subnet. To ensure reliable multichannel performance, TrueNAS recommends placing each interface on a different subnet.
Where does this advice come from?
AFAIK, Samba on Linux has no problems with multiple interfaces on the same subnet, and Windows definitely works correctly that way too (this is MS’s modern advice for a multi-interface file server, since unlike a LAG/NIC team, SMB3+ will multi-session across the NICs for better throughput). Competing NAS systems (Synology for sure) support SMB-MC with multiple NICs on the same network using the same subnet.
The version of Samba included with 25.10.x is v4.22.x which would normally enable SMB-MC by default (it’s been on by default in Samba starting with v4.15.x).
I don’t actually need it at the moment as my NAS has a 10Gb port but most clients are only 1Gb… but I do have 2x10Gb on the NAS, and I have at least one 10Gb-capable client. I was considering plugging both server interfaces in if I could properly use SMB-MC. This “use different subnets” thing would not work for me at all as the clients and NAS are all on the same subnet and L2 segment.
From what I remember when I did the research, years ago, to setup SMB Multichannel on my network, is it linked to how TrueNAS choose the output port.
I could only find this reference on it.
But there was other discussions about setting up multiple interfaces and having them on the same subnet was not recommended, not just in TrueNAS but Linux as well.
All Unixes. (except Solaris 10 & 11 in an IPMP group), route same sub-net packets out through one network interface. To have balanced traffic, you need different subnets.
There is a lot of discussion that things can be setup different. Or that it works different, (for MS-Windows or something else). But, reality is at the moment, multiple physical network interfaces on the same sub-net does not route as you might expect. This is from the old forum, but nothing has changed:
