The first time we used the Storage QoS capabilities in Windows Server 2012 R2 it was done in a trial and error fashion. We knew that it was the new VM causing the disruption and kind of dropped the Maximum IOPS to a level that was acceptable. We also ran some PerfMon stats & looked at the IOPS on the HBA going the host. It was all a bit tedious and convoluted. Discussing this with Senthil Rajaram, who’s heavily involved with anything storage at Microsoft he educated me on how to get it done fast & easy.