Hi,

one question about SMB3 multichannel that has been bothering me today and for which I could not find a definitive answer after some extensive research online is this:

What actually happens if a SMB3 multichannel compatible client (e.g. Windows 10, 8 etc.) with two (or more) gigabit NICs tries to transfer files to / from a SMB3 mulitchannel compatible server (e.g. Windows Server 2012R2) connected via 10Gbe to the same network, e.g. via a switch offering both gigabit and 10Gbe ports? Will the client be able to fully saturate all the gigabit NICs like it actually would do in case of the server having multiple (two or more) gigabit links? Or will SMB3 multichannel not work in this case, as client and server have network adapters of different speeds?

I am aware that SMB3 multichannel will not work with network adapters of different speeds on the same client, e.g. a client with a 100Mbit and 1Gbit NIC installed. But what about the client - server scenario explained above? Is SMB3 multichannel 'intelligent' enough to saturate multiple, slower NICs on the client side knowing that the fat pipe on the server side can handle it?

Thank you!

If there are multiple channels and multiple TCP streams open, then the theoretical possibility exists.  Let's look at two 1 GE NICs on the client and two 10 GE NICs on the server (you won't get multichannel if a single NIC exists on the server).  If you try something like copying a file - there is a single TCP stream, so only one of the NICs will be used.  If you try to copy two files from two different processes, you should theoretically get almost 1 G of traffic on each of the client's NICs.  I say theoretically because file copies are not very good at saturating a link, so you would need some sort of application that can push the limit on more than one TCP stream.

First of all, thank you very much for the quick reply Tim, appreciated.

So if I understand you correctly, SMB multichannel between multiple gigabit links on the client side and just one 10Gbe link on the server side is not going to work? So to (theoretically, of course) fully saturate two gigabit links on the client side, you need 2 x 10Gbe links on the server side? Furthermore, if, for example, the client has a quad gigabit NIC installed, while the server has 2 x 10GBe, only two of those four gigabit links on the client side are going to be saturated with SMB3 multichannel?