In your parameter file you are asking for Vdbench to replay the workload of device 1138166343440 on a concatenated volume consisting of sd1 and sd2.
What makes you think that the replay is not using sd2? Are ANY ios reported on sd2.html?
Could it be that 99.9999% of the i/o is done to sd1, so you really don't see --much-- activity to sd2?
Please include a copy of logfile.html. There is a lot of detailed information there to show how much i/o was traced and how much i/o will be eplayed on which SD.
Apologies I did not realize that is was a concatenated volume consisting of sd1 and sd2. What I was trying to do was put 100% of the load from device 1138166343440 down sd1 and also 100% of the load down sd2 to compare how the two luns perform under the same workload. I am guessing I need two separate parameter files to achieve this?