One backup solution long available on Unix systems will soon be available in the Windows world, in the next version of Windows NT Server. It's called clustering , and it involves linking multiple servers together in a manner that allows them to operate as if they were a single machine. The documents and resources that users request keep getting served, and the systems administrators can go about the business of repairing the first server's problems. To a degree, yes, with a technology known as server mirroring. But server mirroring is costly and inefficient.
Clustering is different.
Each server in a cluster can operate on its own, thus ensuring that the investment it represents is put to its best use. In that way, a cluster operates like a well-trained employee task force, in which members work on their own assignments and pick up an absent member's assignments until everyone is back in place. Clearly, that is a much more cost-effective solution than having staff sitting around doing nothing, kicking into action only if someone is unavailable. How Clusters Work Clusters work primarily through mutual distrust. All the servers in the cluster keep polling each other to see if each one is working, and if something isn't right, the fail-over mechanisms leap into action.