Chapter 3 summarized the architecture, configurations, and benefits as well as caveats of putting storage on an existing network using NAS storage devices. NAS can use existing network resources and excels in addressing large-scale data access read-only applications. However, it is limited by its file-oriented I/O architecture that limits this storage networking solution when addressing heavy online transactional processing (OLTP) applications.
An alternative to NAS is the other cornerstone of storage networking, the Storage Area Network (SAN). SANs, like their counterparts in NAS, allow storage to be connected to a network and provide access to multiple clients and servers. The fundamental differences are the methods in which they accomplish this. SANs require their own network to operate , which provides a significant increase to throughput. SANs also provide direct I/O access from the devices connected to the network, thus providing yet another fundamental shift in distributing the I/O workload among applications.
This chapter will discuss the fundamental concepts of the Storage Area Network as well as providing an insight into the evolution of distributing I/O operations within and throughout processing configurations. Because SANs fundamentally shift the I/O architecture of processing configurations by moving direct storage operations to a network, its important to understand a holistic picture of how these complex technologies developed. Within this chapter is a brief discussion of the evolutionary ancestors of the SAN, most of which have not been rendered obsolete or extinct. Many of the solutions may be configurations installed within your data center.