Implementation and Evaluation of iSCSI over RDMA

Abstract

The Internet small computer systems interface (iSCSI) is a storage network technology that allows block-level access to storage devices, such as disks, over a computer network. Because iSCSI runs over the ubiquitous TCP/IP protocol, it has many advantages over proprietary alternatives. Due to the recent introduction of 10 gigabit Ethernet, storage vendors are interested in the benefits this large increase in network bandwidth could bring to iSCSI. To make full use of the bandwidth provided by a 10 gigabit Ethernet link, specialized remote direct memory access (RDMA) hardware is being developed to offload processing and reduce the data-copy-overhead found in a standard TCP/IP network stack. This paper focuses on the development of an iSCSI software implementation capable of supporting this new hardware, and a preliminary evaluation ofits performance. We describe an approach used to implement iSCSI extensions for remote direct memory access (iSER) with the UNH iSCSI reference implementation. This involved a threestep process: moving UNH-iSCSI software from the Linux kernel to user-space, adding support for the iSER extensions to the user-space iSCSI, and finally moving everything back into the Linux kernel. Results are given that show improved performance of the completed iSER-assisted iSCSI implementation on RDMA hardware.