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Clustering is any technology that enables two or more servers to appear to clients as a single system.

Microsoft Cluster Server (MSCS) is a two-node clustering solution included in Microsoft Windows NT Server, Enterprise Edition.

How Clustering Works

A cluster consists of two or more nodes connected to a shared file system. Each of the nodes is a fully functional computing platform, and the shared file system consists of a hard disk system or RAID-5 array connected to each node using a fast Small Computer System Interface (SCSI) bus or fibre channel connection. The result is a cluster of computer systems that acts and functions as if it were a single system. This provides fast, uninterrupted service for high-demand environments with minimal downtime.

Clustering solutions fall into three different categories:

  • Active/active clustering: This type of clustering makes the most efficient use of system resources because there are no redundant nodes: all nodes run active processes. If one node of a cluster fails, other nodes take on the workload of the failed cluster. The latency for failover in this scenario is typically 15 to 150 seconds, depending on the hardware/software configuration. This is the kind of clustering supported by MSCS. 
  • Active/standby clustering: Nodes are paired within a cluster, with one node designated to take over should another node fail. If an active node fails, a standby node assumes its workload. Latency for failover is also 15 to 150 seconds. 
  • Fault-tolerant clustering: Nodes are paired within a cluster, and all nodes perform all tasks simultaneously. This is an expensive solution from a hardware point of view, but latency for failover is reduced to a second or less.

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