VMware VSAN has a number of features to like – some of these include complete integration with vSphere and vCenter, utilization of unused storage capacity on servers, ability to leverage higher local I/O bandwidth within servers to deliver higher throughput, as compared with SAN or network bandwidth. In addition, use of Flash improves the performance for hot data, and a number of reliability and availability features protect against loss of data.
The feature that impresses me most is the ability to aggregate unused storage pools across physical servers, while providing superior I/O performance as compared with traditional Enterprise storage technologies. SAN is limited to 16 Gb/s, and NAS and iSCSI are currently limited to 10Gb/s (which could go up to 40Gb/s soon. However, internal throughput to disks is much higher, and it is aggregated across servers. The addition of Flash based storage boosts this to much higher levels.
Being able to seamlessly manage this storage pool as a standard VMware datastore, and using it for VMs to provide a high level of service and performance is one of the most invaluable features of VSAN. This feature is already available with products using converged architectures, and will hopefully become a standard feature of the next generation of server hardware.