| Future Directions
Our first product is clearly missing some key features to enable the top-level goal of “just plugging in another system”, when increased performance is needed. Our base design supports larger clusters, but the test and verification effort made it necessary to constrain the initial release to two nodes. We will use a hierarchical approach to clusters with more than N nodes, where N will depend on the communications overhead. Finding and binding to services easily and transparently will be solved using a two-tiered approach consisting of a global directory service coupled with a highly dynamic, cluster specific service. Coarse grain load balancing software will provide the directory with the names of the systems to which incoming clients can connect. Truly distributed applications will be supported by exposing a set of cluster-wide communication and transaction services. Changes to the NT networking architecture are in design to enable low latency, high bandwidth cluster interconnects such as Tandem’s ServerNet [4] and Digital’s MemoryChannel [5].
These interconnects are capable of transferring data directly to and from the application data buffers and eliminate the need for and overhead associated with traditional network stacks. Very high performance shared nothing clusters require some form of I/O shipping, where I/O requests are sent by the cluster communication service to the system physically hosting the disk drive.
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