A typical Novell Cluster Services cluster (see Figure 1-1) consists of a number of machines that coordinate through computer networks to make resources highly available. Nodes in a cluster can be physical, virtual, or any combination of the two. The cluster resources often reside on shared storage.
Figure 1-1 Typical Cluster Configuration with Virtual and Physical Machines
A typical ESXi host machine includes virtual network switches, disk mappings, and virtual machines. A virtual machine can access the network directly through PCI pass-through, or through virtual switches inside the ESXi host.
Just like other Linux systems, shared storage is presented in ESXi hosts as devices. Disk mapping provides a way for virtual machines to share those devices. Clustering of virtual machines normally requires the mappings of shared devices to be Raw Disk Mappings (RDM). The RDMs cannot reside on a datastore on shared devices, unless you have lower-level cluster software to manage the datastore.
From the NCS point of view, there is no difference between a virtual machine and a physical machine. You can cluster any combination of them. Although NCS supports clustering mixtures of physical machines and virtual machines, it is easier to manage clusters where all nodes have the same or similar capacity.