SAN Explained - Storage (or System) Area Networks

Fibre Channel Switches
Fibre Channel Switches. Terry Healy / Getty Images

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) designed to handle 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 work differently than mainstream client-server networks due to the special nature of their workloads. For example, home networks normally feature users browsing the Internet, which involve relatively small of amounts of data triggered at varying times, and can resend some requests if they happen to get lost. Storage networks, by comparison, must handle very large amounts of data generated in bulk requests and cannot afford to lose any of the data.

A system area network is a cluster of high performance computers used for 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 been widely used in SANs and competed with each other for many 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 plus Fibre Channel HBAs (host bus adapters) that connect these switches to server computers.

FC connections provide data rates between 1 Gbps and 16 Gbps.

iSCSI was created as 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 who usually do not have staff trained in the administration of Fibre Channel technology. On the other hand, organizations already experienced in Fibre Channel from history may not feel compelled to introduce iSCSI into their environment. An alternative form of FC called Fibre Channel over Ethernet (FCoE) was developed to lower 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. In addition to FC switches and HBAs, vendors also sell storage bays and rack enclosures for the 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 be integrated fairly easily into home computer networks.