As its name implies, a SAN is its own network, almost always based on fiber channel technology. Fiber channel technology is capable of very high bandwidths, matching the ability of high-performance disk drives to transfer data at their highest sustained rates. But unlike computer buses and SCSI chains, fiber channel can be extended to very large campuses. A SAN based on 9mm fiber optics can extend to a 10km diameter. Keep this thought in mind when I discuss backup and disaster recovery.
SANs normally contain storage devices, servers, and switches.
The SAN switches are capable of connecting every server to every storage device on the SAN, at fiber channel speeds. At this point, you are probably thinking of a number of advantages that a SAN could bring to a large, busy data warehouse. Above all, a SAN offers very high data transfer rates from disk to server and directly from disk to disk. SANs transfer data at 100MBps, with promises in the near future ranging up to 400MBps. A typical data warehouse operation is bottlenecked by two, or possibly three, major data transfer steps.