Performance of optimized software implementation of the iSCSI protocol

The advent of IP-based storage networking has brought specialized network adapters that directly support TCP/IP and storage protocols on the market to get comparable performance that specialized high-performance storage networking architectures provide.This paper describes an efficient software implementation of the iSCSI protocol with a commodity networking infrastructure. Though several studies have compared the performances of specialized network adapters and commodity network adapters, our iSCSI implementation eliminates data copying overhead unlike straightforward iSCSI implementations used in previous studies. To achieve it, we modified a general-purpose operating system by using techniques studied for improving TCP performance in the literature and features that commodity Gigabit Ethernet adapters support. We also quantified their effects.Our microbenchmarks show, compared with a straightforward iSCSI driver that does not use these techniques, the iSCSI driver with these optimizations reduces CPU utilization from 39.4% to 30.8% when writing with an I/O size of 64 KB. However, when reading, any performance gain is negated due to the high cost of operations on the virtual memory system.