Windows 2008 Improvements in Clustering and Storage Area

Improvements in Clustering and Storage Area
Network Support
Although clustering of servers has been around for a long time in Windows (dating back
to Windows NT 4.0 when it was available, but really didn’t work), clustering in Windows
2008 now not only works, but also provides a series of significant improvements that
actually make clustering work a whole lot better.
As IT administrators are tasked with the responsibility of keeping the network operational
24 hours a day, 7 days a week, it becomes even more important that clustering works.
Fortunately, the cost of hardware that supports clustering has gotten significantly less
expensive; in fact, any server that meets the required specifications to run Windows Server
2008, Enterprise Edition can typically support Windows clustering. The basic standard for
a server that is used for enterprise networking has the technologies built in to the system
for high availability. Windows Server 2008, Enterprise Edition or Datacenter Edition is
required to run Windows 2008 clustering services.
Clustering is covered in detail in Chapter 29, “System-Level Fault Tolerance
(Clustering/Network Load Balancing).”
No Single Point of Failure in Clustering
Clustering by definition should provide redundancy and high availability of server
systems; however, in previous versions of Windows clustering, a “quorum drive” was
required for the cluster systems to connect to as the point of validation for cluster opera-
tions. If at any point the quorum drive failed, the cluster would not be able to failover
from one system to another. Windows 2008 clustering removed this requirement of a
static quorum drive. Two major technologies facilitate this elimination of a single or
central point of failure, which include majority-based cluster membership verification and
witness-based quorum validation.
The majority-based cluster membership allows the IT administrator to define what devices
in the cluster get a vote to determine whether a cluster node is in a failed state and the
cluster needs to failover to another node. Rather than assuming the disk will always be
available as in the previous quorum disk model, now nodes of the cluster and shared
storage devices participate in the new enhanced quorum model in Windows 2008.
Effectively, Windows 2008 server clusters have better information to determine whether it
is appropriate to failover a cluster in the event of a system or device failure.
The witness-based quorum eliminates the single quorum disk from the cluster operation
validation model. Instead, a completely separate node or file share can be set as the file
share witness. In the case of a GeoCluster where cluster nodes are in completely different
locations, the ability to place the file share in a third site and even enable that file share
to serve as the witness for multiple clusters becomes a benefit for both organizations with
distributed data centers and also provides more resiliency in the cluster operations compo-
nents.