iSCSI SANs

What are iSCSI SANs?

An iSCSI SAN is a storage area network that makes use of the internet protocol (IP) based standard, iSCSI (Internet Small Computer System Interface) to link data storage facilities. The SCSI (Small Computer System Interface) standard itself was developed to physically connect and transfer data between computers and peripheral devices. iSCSI makes use of the ubiquity and ability of IP networks to carry SCSI commands, enabling the management and transfer of storage data over local area networks (LANs), wide area networks (WANs) and the Internet.

In an iSCSI SAN, operating systems generate the appropriate SCSI commands and data requests in response to end-users or applications, these then go through encapsulation and, if necessary, encryption procedures. Packet headers are added before the resulting IP packets are transmitted over an Ethernet connection. When packets are received, they are decrypted (if required) and disassembled, separating SCSI commands and requests. The SCSI commands are sent on to SCSI controllers and from there to SCSI storage devices. Because iSCSI is bi-directional, the protocol can also be used to return data in response to original requests.

The storage system in an iSCSI SAN is usually referred to as a target and is accessed by other systems across the network via iSCSI initiators; these can be either software initiators embedded within the host operating system or hardware initiators in the form of host bus adapters (HBA’s). The benefit of using hardware initiators is the ability of some HBA’s to offload the TCP/IP activity on to the card, reducing the overhead on the host CPU. These HBA’s are also referred to as TCP Offload Engines or ‘TOE cards’.

iSCSI is a popular SAN protocol, within tier 2 and tier 3 data centres in large organisations, in the core of data centres for small/medium enterprises and also in remote offices, as it can be run over long distances using the existing network infrastructure, unlike traditional Fibre Channel, which requires special-purpose cabling. This has led to the quick growth of iSCSI and it being usually chosen for environments that Fibre Channel has had difficulty penetrating, due to cost, complexity, functionality or support issues.

Its popularity has not only been driven by the fact that organisations can deploy robust affordable SAN solutions on x86 server platforms, but also because even entry level iSCSI disk arrays usually include sophisticated data management capabilities, such as point in time copy, remote copy, thin provisioning and asynchronous mirroring. It is these features that allow organisations to significantly improve storage provisioning, back up and disaster recovery whilst reducing infrastructure and management costs. Making the iSCSI protocol a key technology in helping to bring about the rapid development of the SAN market, by increasing the capabilities and performance of storage data transmission.

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What are iSCSI SANs?