Experimental and theoretical analysis of storage friendly TCP performance in distributed storage area network

Fibre channel storage area networks (SAN) are widely implemented in production data center environments. Recently the storage industry has moved towards deployment of distributed SANs (DSAN), geographically dispersed across large physical distances. In a distributed SAN, specialized gateway devices interconnect the individual Fibre Channel fabrics over IP networks using TCP/IP based protocols (iFCP, FCIP) or over metro to long distance optical networks such as DWDM using native Fibre Channel ports supporting large numbers of link credits. When using TCP/IP based storage networking protocols to interconnect local FC fabrics in a distributed SAN, the sustained throughput achievable depends upon the link characteristics and TCP/IP stack implementation. Sustaining maximum possible storage traffic throughput across the wide area network enables practical distributed SAN deployments by maintaining the required site to site service level agreements. This study explores the effects of several TCP/IP modifications known as storage friendly on sustained traffic throughput for a distributed SAN interconnected via iFCP gateways across an impaired network. The TCP/IP stack modifications include changes to the window scaling, congestion avoidance, and fast recovery algorithms. The theoretical background and experimental results are presented to explain and illustrate these modifications.