Information Technology Reference
In-Depth Information
version of Windows Server you're using. The VM must have access to all the same storage loca-
tions as the physical machine. The VM must also have access to the same pair of networks used
by the physical machine for production and heartbeat communication, respectively.
The advantage to implementing a physical-to-virtual cluster is the resulting high availability
with lower cost. Physical-to-virtual clustering, because of the two-node limitation of VM clus-
tering, ends up as an N+1 clustered solution, where N is the number of physical servers in the
environment and the 1 represents one additional physical server to host the VMs. In each case,
each physical VM cluster creates a failover pair. With the scope of the cluster design limited to
a failover pair, the most important design aspect in a physical-to-virtual cluster is the scale of
the host running the ESXi host. As you may have i gured, the more powerful the ESXi host, the
more failover incidents it can handle. A more powerful ESXi host will handle multiple physical
host failures better, whereas a less powerful ESXi host might handle only a single physical host
failure before performance levels experience a noticeable decline. Figure 7.11 shows an example
of many-to-one physical-to-virtual clustering.
Figure 7.11
Using a single pow-
erful ESXi system
to host multiple
failover clusters
is one use case for
physical-to-virtual
clustering.
esxi-05.lab.local
VM3
VM2
VM1
Shared
datastores
OS Clustering Is Not Limited to Windows
Although we've discussed only Windows Server-based OS clustering methods in this section, you
are not limited to Windows to use OS clustering. Other supported OSes also off er ways to provide
high availability within the OS itself.
