Information Technology Reference
In-Depth Information
First, though, let's start with a well-known technique for achieving high availability at the OS
level: OS clustering, specii cally clustering Microsoft Windows Server instances.
Clustering VMs
Because Windows Server is widely used in corporate and enterprise datacenters today, it's
quite likely that at one point or another you've been asked to create or support a Windows-
based cluster. There are two primary ways to use clustering to provide high availability for
Windows Server:
Network Load Balancing (NLB) clustering
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Windows Server Failover Clustering (WSFC)
While both of these methods are described as clustering, they each target very different pur-
poses. NLB typically provides scalable performance, while WSFC usually focuses on providing
redundancy and high availability in the form of active/passive workload clustering.
Some experts say that vSphere HA eliminates the need for WSFC because—as you'll see later
in this chapter in the section “Implementing vSphere High Availability”—vSphere HA can pro-
vide failover in the event of a physical host failure. That's true, but it's important to understand
that these high-availability mechanisms operate at different layers (refer back to Figure 7.1).
WSFC operates at the OS layer, providing redundancy in the event that one of the OS instances
in the cluster fails. That OS failure could be the result of hardware failure. vSphere HA (and
vSphere FT) operate at a layer beneath the OS and don't operate in exactly the same way. As
we'll reiterate throughout this chapter, each of the high-availability mechanisms described in
this chapter has advantages and disadvantages. You'll want to be sure you understand these so
that you can choose the right approach for your specii c environment.
Table 7.1 provides a quick overview of the clustering support provided by the various ver-
sions of Windows Server.
Table 7.1:
Windows Server 2003/2008 clustering support
Network Load
Balancing
Operating System
Windows Failover Clustering
Windows Server 2003/2008
Web Edition
Yes (up to 32 nodes)
No
Windows Server 2003/2008
Standard Edition
Yes (up to 32 nodes)
No
Windows Server 2003/2008
Enterprise Edition
Yes (up to 32 nodes)
Yes (up to 8 nodes in 2003 and 16 nodes
in 2008)
Windows Server 2003/2008
Datacenter Edition
Yes (up to 32 nodes)
Yes (up to 8 nodes in 2003 and 16 nodes
in 2008)
Windows Server 2012
Yes (up to 32 nodes)
Yes (up to 64 nodes)
