Storage Over IP: When Does Hardware Support Help?

This paper explores the effect of the current generation of hardware support for IP storage area networks on application performance. In this regard, this paper presents a comprehensive analysis of three competing approaches to build an IP storage area network that differ in their level of hardware support: software, TOE (TCP Offload Engine) and HBA (Host Bus Adapter). The software approach is based on the unmodified TCP/IP stacks that are part of a standard operating system distribution. For the two hardware-based approaches (TOE, HBA), we experimented with a range of adapters and chose a representative adapter for the current generation of each of the hardware approaches.

The micro-benchmark analysis reveals that while hardware support does reduce the CPU utilization for large block sizes, the hardware support can itself be a performance bottleneck that hurts throughput and latency with small block sizes. Furthermore, the macro-benchmark analysis demonstrates that while the current generation of the hardware approaches may have the potential to provide performance improvements in CPU-intensive applications, overall the analysis does not demonstrate any performance benefits in database, scientific and email benchmarks. The analysis in this paper points out that a disparity in the processing power between the host and the adapter is the primary cause of the performance bottleneck in the current generation of the hardware approaches. The paper aims to guide the designers of the next generation of hardware-assisted adapters to better leverage the increasing processing power in the host. In particular, future adapters should be capable of handling small operations at wire speed.