Over the past decade, storage area network (SAN) has evolved greatly in terms of its scalability and performance. The fiber channel (FC) SAN and Internet Small Computer System Interface (iSCSI) SAN are being deployed by enterprises around the globe. Although iSCSI technology has been around for almost a decade, FC SAN dominates the storage domain due to the following reasons:
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• iSCSI technology uses local area network (LAN) for connectivity between servers and storage systems and is more cost effective than FC SAN. However, due to latency associated with LAN, iSCSI SAN is not recommended for applications that rely on low response times.
• An iSCSI SAN is not recommended for enterprises than do not have a dedicated LAN infrastructure for connectivity between servers and storage systems.
• iSCSI technology does not support connectivity between the islands of SAN due to network latency.
• A SAN using iSCSI technology is not recommended for disaster recovery (DR) setups, where the recovery point objectives and recovery time objectives are almost zero. Also, many DR applications do not support iSCSI technology.
• iSCSI technology cannot be used in areas where boot from SAN is required, unless every server’s network interface controller card is replaced by iSCSI host bus adapter, which is costlier than FC host bus adapter.
• Storage systems that leverage iSCSI technology have capacity limitations, and cannot be used for requirements exceeding hundreds of Petabytes.
• SAN setups based on iSCSI technology could face blockages in the case of input/output extensive applications; hence, iSCSI SAN should be avoided for billing and banking applications.
• The iSCSI SAN should not be deployed for applications having high data throughput requirements such as batch processing.
• An iSCSI SAN is unable to connect servers to storage in a local data center.
• iSCSI technology cannot be used to merge to SAN.
• The iSCSI SAN cannot be used where the application server memory and central processing unit (CPU) resources are highly utilized. This is due to the fact that in iSCSI technology, system interconnects move from classical bus to a network structure; iSCSI technology has to be mapped to network transport protocols, therefore requiring CPU cycles for encapsulation.
It is because of the aforementioned factors that iSCSI technology is not widely used in a SAN, but is being utilized by small enterprises due to its cost effectiveness. However, FC over Ethernet is being touted as a technology to look forward to in the SAN domain and one that can overcome the limitations of iSCSI technology.
About the author: Anuj Sharma is an EMC Certified and NetApp accredited professional. Sharma has experience in handling implementation projects related to SAN, NAS and BURA. One of his articles was published globally by EMC, and titled the Best of EMC Networker during last year's EMC World held at Orlando, US.