Storage area network (SAN) - Its types,Architecture,Uses,Working

A storage area network (SAN) is a dedicated high-speed network or subnetwork that interconnects and presents shared pools of storage devices to multiple servers.A SAN moves storage resources off the common user network and reorganizes them into an independent, high-performance network. This enables each server to access shared storage as if it were a drive directly attached to the server. When a host wants to access a storage device on the SAN, it sends out a block-based access request for the storage device.

A storage area network is typically assembled using three principle components: cabling, host bus adapters (HBAs), and switches attached to storage arrays and servers. Each switch and storage system on the SAN must be interconnected, and the physical interconnections must support bandwidth levels that can adequately handle peak data activities. IT administrators manage storage area networks centrally.

Storage arrays were initially all hard disk drive systems, but are increasingly populated with flash solid-state drives (SSDs).

What storage area networks are used for

• Fibre Channel (FC) SANs have the reputation of being expensive, complex and difficult to manage.
• Organizations use SANs for distributed applications that need fast local network performance. SANs improve the availability of applications through multiple data paths. They can also improve application performance because they enable IT administrators to offload storage functions and segregate networks.
• Additionally, SANs help increase the effectiveness and use of storage because they enable administrators to consolidate resources and deliver tiered storage. SANs also improve data protection and security. Finally, SANs can span multiple sites, which helps companies with their business continuity strategies.

How a SAN works

The following is a breakdown of how SAN works:

• When a host wants to access a storage device on the SAN, it sends out a block-based access request for the storage device.
• SCSI commands are encapsulated into FC packets. The host HBA accepts the request and it’s converted from its binary data form to the optical form necessary for transmission on the fiber optic,simultaneously, the request is packaged according to the rules of the FC protocol.
• The HBA transmits the FC request to the SAN.

Depending on the connectivity between the HBA and the fabric switch port, one of the SAN switches receives the request and sends it to the storage processor, which then sends it to the storage device.

Setting up the storage area network

To integrate all components of the SAN, an enterprise first has to meet the vendor’s hardware and software compatibility requirements, including:

• Host bus adapters (firmware version, driver version, patch list)
• Switch (firmware)
• Storage (firmware, host personality firmware, patch list)

Then to set up the SAN:

• Assemble and cable together all the hardware components and install the corresponding software.
• Check the versions.
• Set up the HBA.
• Set up the storage array.
• Change any configuration settings that may be required
• Test the integration
• Test all the operational processes for the SAN environment, including normal production processing, failure mode testing and backup
• Establish a performance baseline for every component as well as for the entire SAN.
• Document the SAN installation and operational procedures.

SAN architecture

SAN architecture is composed of:

• Host layer: The servers and host bus adapters, as well as all the software that runs on the server and allows the HBA to communicate with the fabric layer.
• Fabric layer: All the hosts connect to the storage devices on the SAN through the SAN fabric. The network portion of the SAN is made up of the following fabric components:
• SAN switches; data routers; cables; communications protocol (fabric components communicate via the Fibre Channel communications protocol).
• Storage layer: The storage arrays, including the storage processors.

SAN Types

• Virtual SAN : A virtual storage area network (VSAN) is a software-defined storage offering that is implemented on top of a hypervisor, such as VMware ESXi or Microsoft Hyper-V. Virtual SANs yield a number of benefits, such as ease of management and scalability.For the most part, VSANs are hardware-agnostic. As long as the hypervisor recognizes and supports the storage hardware, the VSAN can use it, although each vendor has its own requirements.
• Unified SAN : Unified SAN is based on the concept of unified storage, which exposes file storage and block storage through a single storage device, usually a modified network-attached storage appliance (NAS appliance).A unified SAN takes this concept a step further by exposing not only dedicated logical unit numbers (LUNs) -- like any other SAN -- but file system-based, NAS-like storage.
• Converged SAN : Storage area networks are normally kept separate from Ethernet networks. A converged SAN uses a common network infrastructure for network and SAN traffic to eliminate redundant infrastructure and to reduce cost and complexity.

SANs often make use of Fibre Channel, whereas data networks are usually based on Ethernet. Converged SANs adopt Fibre Channel over Ethernet (FCoE), which encapsulates FC payloads into Ethernet frames. Converged SANs are almost always based on 10 gigabit Ethernet, and multiple network ports are sometimes bonded together to increase throughput.

SAN pros and cons

The main benefit of using a SAN is that raw storage is treated as a pool of resources that IT can centrally manage and allocate on an as-needed basis. SANs are also highly scalable because capacity can be added as required.