Distributed-and-Split Data-Control Extension to SCSI for Scalable Storage Area Networks

A “Storage-Area Network” (SAN) comprises computers (“Initiators”), storage “block devices” (“Targets”), and a Controller(s). Most SANs use the SCSI protocol over various communication infrastructures. Presently, all Initiator Target traffic must pass through the Controller, severely limiting scalability. We extend the SCSI-3 Transport layer to support distribution, and combine this with SCSI's support for data control split to create DSDC, a novel architecture that can be used over any networking infrastructure: data may be sent directly between Initiators and Targets, relieving the Controller communication bottleneck; the use of multiple paths for data moreover relieves traffic bottlenecks on network links; finally, passing all commands through the Controller retains simplicity. DSDC thus enables the construction of much larger SANs while retaining the simplicity of a single Controller. A prototype SAN using Ethernet and Linux nodes, with DSDC implemented in the iSCSI transport layer protocol and in the Controller’s SCSI application layer, has been constructed.