VMware vSphere Metro Storage Cluster (VMware vMSC) is a configuration option, introduced in vSphere 5, that allows for the use of stretched clusters that are spread across geographical locations. This configuration allows organizations to perform load balancing and nondisruptive live migrations between active data centers.
VMware vMSC can give organizations many of the benefits that a local high-availability cluster provides, but with geographically separate sites. Stretched clustering, also called distributed clustering, allows an organization to move virtual machines (VMs) between two data centers for failover or proactive load balancing. VMs in a metro storage cluster can be live migrated between sites with vSphere vMotion and vSphere Storage vMotion. The configuration is designed for disaster avoidance in environments where downtime cannot be tolerated, but should not be used as an organization's primary disaster recovery approach.
VMware vMSC was introduced in vSphere 5. VMware vMSC is only practical for organizations that require active site balancing and very high availability (HA) standards, because the approach requires a high bandwidth, low latency connection between the two sites. The maximum supported network latency between the two sites is 10 milliseconds round-trip time, which limits the geographic distance in which a stretched cluster will work to less than 100 kilometers, in most cases. vMSC supports Fibre Channel (FC), iSCSI, network file system (NFS) and Fibre Channel over Ethernet (FCoE) protocols, but vMSC links require low latency and high-bandwidth network connectivity for best operation.