There are many differences between Grid and Clusters. The following table shows comparison of Grid and Clusters.
|Population||Commodity Computers||Commodity and High-end computers|
|Discovery||Membership Services||Centralized Index and Decentralized Info|
|Inter-Operability||VIA and Proprietary||No standards being developed|
|Single System Image||Yes||No|
|Capacity||Guaranteed||Varies, but high|
|Speed(Lat. Bandwidth)||Low, high||High, Low|
A cluster is a group of computers organized together to perform the same set of functions. For instance, you may have a cluster running your database software. Or you can have a cluster running your corporate e-mail server software.
A grid is a collection of resources. A grid can be composed of multiple clusters. In Oracle’s grid world, you can have a cluster of servers running the database software and a cluster of servers running the Application Server software. Since they are all in the grid, you can move resources from one cluster to another should demands dictate.
Oracle RAC Cluster Tips by Burleson Consulting