Clustering means different things to different people. For some, it refers to any kind of fault-tolerance system involving two or more systems. For others, it refers specifically to the use of multiple systems to parallelise execution and increase performance. They operate so that users never know which particular node they are accessing. For all intents and purposes, they appear as one device.
Advantages There are many potential advantages of clustering.
It makes a lot of sense to use it, even though it can be expensive. Apart from the fact that you need multiple servers , software for clustering is generally expensive. The first of these applies because servers in a cluster work as backups to any others that go down. If one of the servers dies, the others dynamically take up the slack. On more advanced clusters, this takeover can happen in milliseconds.