Virtualization with prefetching abilities based on iSCSI

Abstract

The Internet-SCSI protocol [iSCSI] allows a client to interact with a remote SCSI-capable target by means of block-oriented commands encapsulated within TCP/IP packets. Thereby, iSCSI greatly simplifies storage virtualization, since clients can access storage in a unified manner, no matter whether the I/O-path is short or long distance. Intermediate devices located on the path between a client and a target can easily intercept iSCSI sessions and rewrite packets for the sake of load balancing, prefetching, or redundancy, to mention just a few beneficial applications. Within this paper we describe the design and implementation of such an iSCSI capable intermediate device that deploys prefetching strategies in combination with redundant disks to reduce average I/O-latency. Depending on its location within the network, this virtualization and prefetching device can hide wide area access latency and reduce network contention targeting remote SCSI-devices to a large extent.