What is a SAN (Storage Area Network)?

What is a SAN?

A Storage Area Network (SAN) is a centrally managed, high-speed storage network consisting of one or more vendor storage systems, storage management software, application servers and network hardware that allows users to access and utilize business information data. A SAN storage platform presents pools of raw data to a server infrastructure over a dedicated network connection.

SAN Storage Hardware

SAN devices are usually connected by independent high-speed iSCSI or Fibre Channel (FC and FCoE) network protocol hardware. Fibre Channel connectivity enables immensely fast data throughput between the storage array and the attached server device(s). Typically, the data transfer speeds of fibre-channel SAN storage start at around 4 Gbps, ranging up to 128 Gbps and faster. Speed varies by vendor and the type of SAN technology infrastructure, but the very latest storage fabric can now break 200 Gbps transfer rates. This allows the attached servers to be presented with a storage LUN, or storage volume, that performs as if the data disks were directly attached storage (DAS).

SAN storage is compatible with physical and virtual server infrastructure. A SAN is connected to a physical server or physical ESX (virtual) host either directly using Fibre Channel cables or through a SAN Switch (again, with Fibre Channel or Fibre Channel over Ethernet cabling). Each host server must have at least one, but usually two, HBAs (host bus adapters) for a resilient connection to the storage. An HBA is an installable hardware storage controller card. Many server manufacturers include HBA connections directly on system boards; however, it is common practice to purchase additional high-speed HBA riser cards to pair with the SAN fabric and storage devices in the host environment.

A SAN Switch (or Fibre Channel switch) is a part of the Storage Area Network fabric which enables the storage to communicate over the network. The SAN storage usually plugs directly into an FC SAN Switch using Fibre Channel cabling and SFP modules. The rest of the enterprise network fabric will also route via the FC SAN, switch allowing the storage to be presented to each individual server. This connectivity will either be via a directly attached (redundant) fibre connection, or via ultra-high-speed InfiniBand network fabric connections.

How Does a SAN Work?

A SAN uses block level storage functionality to present raw storage to a logical unit (LUN) which is then presented to a target device. A LUN is a block of raw data, which can vary in size significantly, but is usually made up of a group of disks and presented to a target as a LUN in RAW state. Unlike an NAS, where data is presented to the operating system in a readable format, the LUN can only be read by a storage controller and interpreted by the operating system software-based initiator. A LUN requires an initiator on the host operating system to attach the LUN, such as the Microsoft iSCSI initiator configuration tool. Each LUN is given a unique identifier by the SAN, and the server’s hardware controller and the software initiator must be configured with the same LUN ID to interact with the raw data.

The Future of SAN Storage

SAN storage has been present in data centers around the world for several decades. Storage vendors continually improve features and add new features to benefit modern hyper-converged data centers. Scalability, manageability, and efficiency are the key areas of continued improvement, according to Network World. Organizations demand increasing data availability; therefore, SAN storage must scale as an organization grows. There are two key technologies which are becoming more common in modern SAN storage devices:

Unified SAN Storage

Traditionally, SAN storage exclusively used block-level data architecture; today, this definition is changing, and often you will find a SAN storage device which is classed as “Unified” SAN Storage. This means the storage is consolidated and can be used for block level SAN storage, NFS file level NAS storage and Object-Level data objects. Essentially, unified storage gives the ultimate flexibility for managed service providers and offers users a more general-purpose SAN storage device. EMC VNX and Netapp Filers are good examples of unified SAN storage.

Converged Storage

Another emerging technology which is likely to influence SAN storage design in the future is converged storage appliances. These devices combine storage and compute nodes into one modular package. Essentially, they are servers with plenty of storage directly attached, but with a software layer over the hardware to present the device as a storage node. VMware vSAN is an example of how converged storage is growing in popularity.

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