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 SCSIs 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.