4.3.3 Storage I/O Control
Storage I/O Control (SIOC) manages storage resources across hosts through storage device latency monitoring and disk shares that are enforced at the datastore level. Preventing imbalances of storage resource allocation during times of contention protects virtual machine performance in highly consolidated, virtualized environments.
Enabling SIOC on all datastores in a cluster results in lower worst-case device latency by maintaining a balance between workload isolation/prioritization and storage I/O throughput. For more information, see Storage I/O Control Technical Overview and Considerations for Deployment (http://www.vmware.com/files/pdf/techpaper/VMW-vSphere41-SIOC.pdf). SIOC does not support raw device mapping (RDM) or datastores with multiple extents. If you are using datastores backed by arrays with automated storage tiering, validate compatibility with SIOC.