Pictures best explain AMP clustering. The following figure illustrates a situation in which fallback is present with one cluster, which is essentially an unclustered system.
Note that the fallback copy of any row is always located on an AMP different from the AMP which holds the primary copy. This is an entry-level fault tolerance strategy. In this example which shows only a few rows, the data on AMP3 is fallback protected on AMPs 4, 5, and 6. However, in practice, some of the data on AMP3 would be fallback protected on each of the other AMPs in the system. The system becomes unavailable if two AMPs in a cluster go down.