SAN Explained — Storage (Or System) Area Networks

The term SAN in computer networking most commonly refers to storage area networking but can also refer to system area networking.

A storage area network is a type of local area network (LAN) that handles large data transfers and bulk storage of digital information. A SAN typically supports data storage, retrieval and replication on business networks using high-end servers, multiple disk arrays and interconnect technology.

Storage Networks vs. Client-Server Networks

Storage networks work differently from mainstream client-server networks due to the special nature of their workloads. For example, home networks normally feature users browsing the Internet, which involves relatively small amounts of data at varying times. They can also resend some requests if they happen to get lost.

Storage networks, by comparison, handle large amounts of data in bulk requests and can't afford to lose any of the data. A system area network is a cluster of high-performance computers. It's suited to distributed processing applications requiring fast local network performance to support coordinated computation and output to external users.

Fibre Channel vs. iSCSI

The two dominant communication technologies for storage networks — Fibre Channel and Internet Small Computer Systems Interface (iSCSI) — have both appeared in SANs and competed with each other for years.

Fibre Channel (FC) became the leading choice for SAN networking during the mid-1990s. Traditional Fibre Channel networks contain special-purpose hardware called Fibre Channel switches that connect the storage to the SAN. Fibre Channel HBAs (host bus adapters) connect these switches to server computers. FC connections provide data rates between 1 Gbps and 16 Gbps.

iSCSI is a lower-cost, lower-performance alternative to Fibre Channel and started growing in popularity during the mid-2000s. iSCSI works with Ethernet switches and physical connections instead of specialized hardware built specifically for storage workloads. It provides data rates of 10 Gbps and higher.

iSCSI appeals especially to smaller businesses that usually don't have dedicated staff to administer Fibre Channel technology. Organizations already experienced in Fibre Channel may not introduce iSCSI into their environment. An alternative form of FC called Fibre Channel over Ethernet (FCoE) lowers the cost of FC solutions by eliminating the need to purchase HBA hardware. Not all Ethernet switches support FCoE, however.

SAN Products

Well-known makers of storage area network equipment include EMC, HP, IBM, and Brocade. Along with FC switches and HBAs, vendors sell storage bays and rack enclosures for physical disk media. The cost of SAN equipment ranges from a few hundred up to thousands of dollars.

SAN vs. NAS

SAN technology is similar but distinct from network attached storage (NAS) technology. While SANs traditionally employ low-level network protocols for transferring disk blocks, a NAS device typically works over TCP/IP and can easily integrate with home computer networks.