Here are 3 good articles written by Michel Roth.
So how do you know if you have a problem? Well on the Terminal/Citrix servers you need to monitor the outstanding Redirector/Current Commands queue. The goal of a Terminal/Citrix Server deployment is to keep the Current Commands value to about 60 on heavily utilised servers. A Current Commands value of 80 means that on average you’ve got 80 pending SMB/RPC network I/O commands in the queue. With standard out-of-the-box tuning, it means that you’re probably getting pretty close to the edge at times. But if Current Commands are consistently over 120, then chances are you could have some serious file serving issues too. Note that the Current Commands counter is the sum of commands pending to all servers. When the pending requests queue is full, things stop (pause) momentarily until the queue has free slots. If settings such as the MaxMpxCt and MaxWorkItems values are not increased on the file server(s), anything at all that slows down your file server will potentially impact on your Terminal/Citrix Servers. Tuning MaxCmds on the Terminal/Citrix Server end won’t provide any enhancement unless the file server end is increased as well.
Note that some customers use the MultiUserEnabled value as per Microsoft knowledge base article KB913835. MultiUserEnabled simply increases the number of file handles available per user session. It doesn’t provide any SMB tuning per se.