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How Clustering Works
To understand cluster resources,
it is first necessary to understand how the cluster actually works.
Windows uses Active-Passive clustering, meaning that a cluster resource
is “owned” by only one cluster node at any one time. The
resource can be moved back and forth between cluster nodes as required,
or automatically upon failure. As a simplified example, imagine server
A and server B are clustered, using a quorum disk and a shared disk
N. At any one time, either server A or server B can own and have access
to the N drive. If server A owns the N drive, it is possible to browse
that drive and to use it as a normal drive via Windows explorer on server
A. At the same time, looking in “My Computer” on server B
shows the N drive but attempting to access it produces an error message
stating that the drive is inaccessible. If we then shut down server
A, the N disk cluster resource is automatically failed over to server
B and the above example is reversed.
OS Clustering and Application Clustering
Note: There is an important distinction between the Operating System clustering and application clustering. Whilst Windows only supports Active-Passive clustering, some applications support Active-Active clustering where an instance of the application runs on both cluster nodes simultaneously. Microsoft Exchange is one application that functions in this way. Active-Passive means only one node in the cluster is doing “work” at any one time, active-active means both nodes are doing “work”. If you’re designing a cluster, you need to understand the difference. |
Cluster resources are objects that
represent resources and services the cluster is providing. The cluster
resources themselves are nothing more than representations of the actual
resources and services the cluster is providing. For example, it is
possible to add an IIS web site as a cluster resource. The web site
itself is contained within IIS on the cluster nodes, and the cluster
resource representing it is contained only within the cluster manager.
It is possible to configure NetBIOS names, IP addresses, file shares
and much more as cluster resources.
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CertiGuide to A+ (A+ 4 Real) (http://www.CertiGuide.com/apfr/) on CertiGuide.com
Version 1.0 - Version Date: March 29, 2005
Adapted with permission from a work created by Tcat Houser et al.
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