Distributed storage on networks of Linux PCs using the iSCSI protocol

Abstract

iSCSI is a protocol standardized by IETF that runs on a TCP/IP network to transfer standard SCSI commands. In this paper, we evaluate the performance of iSCSI using standard PCs running a software implementation of the protocol, with the aim of assessing the performance of low-cost distributed storage solutions. First, we compare the performance when using a local disk with those of a virtualized disk connected through a standard gigabit Ethernet LAN during file I/O operations. Then, we emulate the characteristics of a WAN/MAN setup by using a software emulator within the Linux kernel to generate delays and packet losses, and evaluate the ability of iSCSI to offer disaster recovery solutions over high-speed long-distance links. We found that, even if TCP can be tuned to support links with large bandwidth-delay products, iSCSI does not reach good performance due to its windowing scheme that is not large enough, in the used software implementation, to support long-distance links. Finally, we test the iSCSI behavior when other types of traffic share network links with the iSCSI protocol.