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iSCSI is one of the most popular protocols among the SAN (storage area network) working on an IP network. iSCSI is a standard to encapsulate a SCSI command into a TCP/IP packet, thus we can make an access to a storage system with commoditized IP devices only. In this paper, iSCSI sequential write access for a remote backup system is focused. It is well known that iSCSI experiences performance deterioration under a high latency environment. The storage access by iSCSI has multiple hierarchical protocols. Due to this complicated structure, it is very difficult to identify the performance bottleneck that causes the deterioration. Therefore, system tools which can analyze the complicated layered structure are required. We have developed system tools that enable us to monitor the hierarchical protocols. As a result, we have identified the cause of the iSCSI performance degradation problem. We then fixed the problem and confirmed that one can obtain the performance close to the theoretical limit.