Very good article from Greg Schulz (thank you) around VMware vSphere v5 and Storage DRS.
Recently VMware announced version 5.0 of their vSphere virtualization solution with a theme of reducing complexity, enabling automation, and supporting scaling with confidence. As a key component for supporting cloud, virtual and dynamic infrastructure environments, vSphere V5.0 includes many storage related enhancements and new features.
Memory and storage hierarchy
Before going further into why the importance and relevance of storage related enhancements for vSphere V5.0 including DRS, lets take a quick step back to look at the big picture. The storage hierarchy (figure 1) extends from memory inside servers out to external shared storage, including virtual and cloud accessible resources. Often, discussions separate the relationship between physical machine (PM) server memory and data storage as one is considered to be a server topic and the other a disk discussion. However, the two are very much interrelated particularly with virtual machines (VMs) and thus benefit as well as impact each other. Servers need I/O networking to communicate with other servers, with users of information services, and with local, remote, or cloud storage resources.
In figure 1, an example of the storage or memory hierarchy is shown, ranging from fast processor core or L1 (level 1) and L2 (level 2) on-board processor memory to slow, low-cost, high-capacity removable storage. At the top of the pyramid is the fastest, lowest-latency, most expensive memory or storage, which is also less able to be shared without overhead with other processors or servers. At the bottom of the pyramid is the lowest-cost storage, with the highest capacity while being portable and sharable. Read on here