A: Most of us are familiar with VMware DRS, the service that load balances virtual machine (VM) processing among hosts in a cluster. The release of VMware vSphere 5's Storage DRS applies this concept to how VM disk files are managed.
Storage DRS is designed to assist in two high-level use cases. First, it can rearrange the location of VM disk files to ensure that storage consumption is load balanced. As an optional second use case, Storage DRS can rearrange the location of VM disk files to ensure their use is load balanced. This second case seeks to minimize the amount of storage I/O latency, which has a direct impact on VM performance. Load balancing for this second use case is enabled by checking the box marked Enable I/O metric for SDRS recommendations in your storage cluster's SDRS Runtime Rules properties screen.