Aki Tomita

A scalable, cost-effective, and flexible disk system using high-performance embedded-processors

As a scalable, cost-effective, and flexible solution for data-intensive systems, we are exploring active-network-storage (ANS), which is an array of ANS disk drives. The ANS drive improves flexibility by using a modular software design; that is, users can specify functions of the ANS drive by loading/unloading the corresponding modules on it. To keep the ANS drive cost-effective, users are allowed to choose whether native code modules or platform-independent Java-bytecode modules are executed on the drive. We forecast that a current high-performance embedded-processor is powerful enough to enable this modular design to be implemented and to provide a scalable, cost-effective, and flexible ANS system. We have confirmed our forecast by conducting an experiment with an ANS drive prototype with a 200 MHz embedded-processor running database sequential scanning and NFS, which are typical off-loaded functions with different characteristics. To evaluate scalability and cost-effectiveness of the ANS system, we estimated the throughput from measurements on our ANS prototype, and we compared it with the throughput that was measured on a 450 MHz Pentium II Xeon server. Our estimation indicates that the scan throughput of the ANS system increases up to 71 MB/s while that of the server saturates at 25 MB/s because of its CPU bottleneck. The NFS read/write throughputs of two ANS drives surpassed the server maximum throughputs.

Improving design dependability by exploiting an open model-based specification

In an open system standards environment, a formal specification can be shared by all of its implementations, which results in the sharing of development cost. This paper presents a specification-based adaptive test case generation (SBATCG) method for generating validation test cases and a specification-based adaptive consistency check generation (SBACCG) method for generating on-line consistency checks for implementations developed from a model-based specification. The SBATCG (SBACCG) method first derives test cases (consistency checks) through rigorous exploration of a model-based specification, adapts the test cases (consistency checks) to the program structure of a particular implementation, and then produces test cases (consistency checks) that are particularly suitable for the implementation. Testing does not guarantee a programs freedom from faults. The results of the fault-injection experiment show that the SBACCG method can complement the SBATCG method.