SMP machines are easier to control while MPP machines scale much farther. Clusters are groups of machines joined through some type of high-speed network like connection. The relative advantages of SMP versus MPP are best left to another discussion. However, the advantages of clustering are worth discussing. The range of query loads in a data warehouse is truly astounding.
Some queries take micro-seconds and some take hours.
The data load process itself is usually an infrequent process that is composed of a small number of very large complex processes. Clustering will allow you to create a large cluster to process unusual high demand periods. This might be the data load process, or it might be the peak that one sees at quarter end. This section summarizes some approaches that we assume will always be in place. This can have significant impact on the storage required for both the data and the indexes.