Storage Area Network

Storage Area Network or popularly known as SAN are specialized high speed, high availability (dedicated network of servers) and shared storage devices that use fiber channel technology to connect servers to storage disks. It enables sharing of the storage resources across multiple servers. And helps to connect all servers across the globe of related network, lets them to be managed centrally with effective maintenance & protection of data.

The classification of SAN’s ” Storage Area Network “is based on the protocols supported by respective SAN’s as:

FC SAN (Fibre Channel SAN Storage Area Network ) where it uses Fibre channel protocol for the communication between servers and data storage devices. Fibre channel is the high speed network technology using high speed optical cables (for long distance connectivity) & serial copper cables (shorter distance connectivity). It offers the throughput unto 3200 M Bytes/sec means 16 G Bytes per second without dropping frames. These are highly scale-able and can accommodate 15 Million devices. The components are Nodes, Cables, Connectors (standard, lucent & straight tip), Interconnection devices (FC Hubs, Switches & Directors) & management software. The FC inter-connectivity supports point to point ( P2P ), Fibre Channel Arbitrated Loop (FC-AL), Fiber Channel Switched Fabric (FC-SW). P2P offers limited connectivity as only two devices can communicate at any point of time & is not scale-able. FC-AL allows to attachment of devices on share loop using start or ring topology. Only one device can perform I/O at time and can support only 126 devices at a time. Any addition or deletion of node can cause some pause on network traffic. FC-SW allows communication of all nodes on a logical space created on switch or switches with unique domain identifier. The link between the switches is referred as Inter Switch Links (ISL), ISL switches are connected together forming fabric & here nodes are not shared but data is transferred in dedicated path. The different ports used for communication between devices in switched fabric are N, E, F, and G Ports.

  • N Port (Node port) or host port
  • E port (Expansion Port) for connection between two FC Switches
  • F Port (Fabric Port) for connection with N Port
  • G Port (Generic Port) that can work as E or F port

The protocol used is FCP (Fibre Channel Protocol). It is the SCSI interface protocol that defines the high speed data transfer rate hence offers the advantages of channel & network technologies. Here all the devices appear as local devices for the host operating system.

IP SAN (IP based Storage Area Network ) uses IP based protocols for communication by transferring the block level data over the network hence reduce the cost as it will be easy to use the existing networks along with security, disaster recovery etc. The protocols used are iCSI & FCIP. iSCSI connects host & storage by encapsulating the SCSI commands & data into an IP packet and transports them using TCP/IP.

FCoE SAN (Fibre Channel over Ethernet Storage Area Network ) uses FCoE protocol for the communication that helps to transfer the FC data over network. FCoE consolidates LAN & WAN traffic over a single physical infrastructure. FCoE is generally applicable for the complex networks.

The major components are Converged Network Adaptors (CNA) that offers the functionality of NIC & FC HBA and contains the separate modules for 10GB Ethernet, FC & FCoE ASICs, and Cables like Twinax & Optical fibre cable, FCoE Switch containing both Ethernet and FC switch functionalities.

Basic Definitions
Node               :  Any device connected to SAN (server, tape drive etc).
W W N           :  World Wide Name is unique identifier used to identify storage devices.
Fabric            : Encompasses all hardware that connects servers and workstations to storage devices through the use of fiber channel switching technology.

Storage Area Network eliminates the restrictions on amount of data that can be accessed by an individual server as oppose to server with direct attached disk. Storage can be accessed by multiple servers simultaneously with more robust faster processing. Storage resources can be centrally managed and storage space can be allocated & de-allocated to hosts needed, Components are hot swapable eliminating down time

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