Evaluation of advanced TCP stacks in the iSCSI environment using simulation model

Enterprise storage demands have overwhelmed traditional storage mechanisms and have led to the development of storage area networks (SANs). This has resulted in the design of SCSI transport protocols that encapsulate SCSI commands and data for transfer over the network. Fiber channel protocol was the first such protocol that used gigabit per second speed links to carry SCSI commands and data over long distances. However, with the emergence of gigabit Ethernet and the iSCSI (Internet SCSI) protocol that maps the SCSI block oriented storage data over TCP/IP and enables storage devices to be accessed over standard Ethernet based TCP/IP networks, reduction in costs and a unified network infrastructure can be achieved. The iSCSI data flow is regulated by the TCP congestion control algorithm. The standard TCP Reno congestion control algorithm substantially under utilizes the network bandwidth over high speed connections for most applications. To address this limitation of TCP, variants of the TCP congestion control algorithm, designed for high bandwidth networks, such as FAST TCP, BIC-TCP, H-TCP, and Scalable TCP have been proposed. We use simulations and experiments to compare the performance of these TCP variants in an iSCSI environment. Our results indicate that H-TCP outperforms the other TCP variants in an iSCSI environment. However H-TCP results in unfair sharing of network bandwidth when simultaneous multiple flows exist. Performance obtained using BIC-TCP is only second to that using H-TCP and it is relatively fairer as compared to H-TCP.