Clustered storage is the use of two or more storage servers working together to increase performance, capacity, or reliability. Clustering distributes work loads to each server, manages the transfer of workloads between servers, and provides access to all files from any server regardless of the physical location of the file.
Two basic clustered storage architectures exist, known as tightly coupled and loosely coupled;
A tightly coupled cluster has a proprietary physical backplane into which controller nodes connect. While this backplane fixes the maximum size of the cluster, it delivers a high-performance interconnect between servers for load-balanced performance and maximum scalability as the cluster grows. Additional array controllers, I/O (input/output) ports, and capacity can connect into the cluster as demand dictates.
A loosely coupled cluster offers cost-effective building blocks that can start small and grow as applications demand. A loose cluster offers performance, I/O, and storage capacity within the same node. As a result, performance scales with capacity and vice versa. Although the clusters can grow quite large in theory, the scalability is limited by the performance of the interconnect and the resulting tradeoffs in communication with the cluster controllers.
Experts cite several trends that have begun to drive a movement toward clustered storage in recent years, including a general shift to cluster computing, an increase in available low-cost, high-speed storage solutions, and explosive growth in the amount of digital content requiring storage.