Analysis of Multiple Target Network Storage Access using Multi-routing VPN Connections Nozomi Chishima Ochanomizu University 2–1–1, Otsuka, Bunkyo-ku Tokyo 112–8610, JAPAN nozomi@ogl.is.ocha.ac.jp Saneyasu Yamaguchi Kogakuin University 1–24–2, Nishishinjuku, Shinjuku Tokyo 163–8677, JAPAN sane@cc.kogakuin.ac.jp Masato Oguchi Ochanomizu University 2–1–1, Otsuka, Bunkyo-ku Tokyo 112–8610, JAPAN oguchi@computer.org Abstract As the introduction of SAN progresses for the purpose of the storage management cost reduction, iSCSI is expected as a representative of IP-SAN that uses IP network. How- ever, SAN is mostly used only in the server site currently. Thus we have claimed iSCSI can be employed in a WAN environment using VPN, as well as in a local environment. In this paper, the behavior of the TCP Congestion Win- dow is observed and the performance of the system is eval- uated when iSCSI access through multiple connections is performed using a multi-routing function of a VPN router. Furthermore, we have examined the iSCSI access method with mutiple connections on VPN when a parallel storage system is used as Target of network storage. 1. Introduction Recently, IP-Storage Area Network (SAN) configured with inexpensive Ethernet and TCP/IP is introduced. As a standard, iSCSI protocol is becoming important in IP- SAN[1][2]. iSCSI encapsulates SCSI command, within a TCP/IP packet and transports the volume of data between server (Initiator) and storage (Target). As the realization of the gigabit/10gigabit class line is expected according to the advancement of Internet, iSCSI will be effective further- more. In the present condition, SAN is mainly used only in the server site. However, SAN is expected to connect between server and storage of a remote site for the sake of remote backup. Thus we have claimed iSCSI used in a local en- vironment can be applied to the WAN using Virtual Pri- vate Network (VPN). Furthermore, we propose the method to build multi-routing connection on the VPN established through WAN, for the realization of higher performance and reliability of the connection. A large-scale storage system consists of multiple storage devices. Such system has a single access interface, single IP address for example, though it contains a lot of storage de- vice actually. In the case of using such a high-performance parallel storage system, including autonomous disks, the network tends to become a bottleneck. Thus the multi- routing access is considered to be effecrive in this case. 2. Background of Our Research Works Target Target Initiator Initiator port=A port=B iSCSIsession TCPconnection 192.168.1.2 192.168.1.1 Figure 1. iSCSI multiple connections iSCSI is the most popular protocol of IP-SAN. iSCSI is a standard to encapsulate a SCSI command into a TCP/IP packet, so we can build SAN only with IP devices when we use iSCSI. On the other hand, it has complicated hierarchi- cal structure. In addition, although iSCSI is expected for the realization of the long-distance remote storage access, it has the problem of Long Fat Pipe in the case of using the giga- bit connection. Therefore appropriate control of the TCP/IP layer is required[3]. iSCSI can be variously tuned. We can establish multi- ple TCP connections in a single iSCSI session by the im- plementation of UNH-iSCSI offered by University of New Hampshire[4], which is used in this experiment. iSCSI stan- dard requires that all iSCSI PDUs related to a single SCSI command must all be sent and received on a single connec- tion. Different read commands in the same session can use different connections. The choice of which connection to use for a command is made by the initiator. The target must always respond to that command on the same connection.