A cluster of virtual machines across physical hosts (also known as a cluster across boxes) protects against software failures and hardware failures on the physical machine by placing the cluster nodes on separate ESXi hosts. This configuration requires shared storage on an Fibre Channel SAN for the quorum disk.
The following figure shows a cluster-across-boxes setup.
Two virtual machines on two different physical machines (ESXi hosts) run clustering software.
The virtual machines share a private network connection for the private heartbeat and a public network connection.
Each virtual machine is connected to shared storage, which must be on a SAN.
A quorum disk can be configured with iSCSI, FC SAN or FCoE. A quorum disk must have a homogenous set of disks. This means that if the configuration is done with FC SAN, then all of the cluster disks should be FC SAN only. Mixed mode is not supported.
Windows Server 2008 SP2 and above systems support up to five nodes (virtual machines). Windows Server 2003 SP1 and SP2 systems support two nodes (virtual machines). For supported guest operating systems see Table 4.
This setup provides significant hardware cost savings.
You can expand the cluster-across-boxes model and place multiple virtual machines on multiple physical machines. For example, you can consolidate four clusters of two physical machines each to two physical machines with four virtual machines each.
The following figure shows how you can move four two-node clusters from eight physical machines to two.