Total High Performance Time and Design of Degradable Real-Time Systems

Masaharu AKATSU  Tomohiro MURATA  Kenzo KURIHARA  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E77-A   No.3   pp.510-516
Publication Date: 1994/03/25
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on the 6th Karuizawa Workshop on Circuits and Systems)
Category: Concurrent Systems, Discrete Event Systems and Petri Nets
availability,  reliability,  performance,  fault-tolerance,  modeling,  Petri nets,  

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This paper proposes the Total High Performance Time as a performance-related reliability measure in degradable/recoverable real-time systems. This measure reflects the effect of system behavior in pending states that are temporary states between the normal state and degraded states where the system operates in a degraded mode as a consequence of component failures. Such systems have to perform not only normal procedures but also error/recovery procedures in pending states, so the performance there is lower than that in the degraded states. In real-time systems, if performance is less than a lower limit, the response time for on-line transactions cannot meet the deadline. The consequences of failing to meet the deadline could be system failure. Therefore, the system reliability is affected significantly by whether the performance there is higher than the lower limit or not. A state where the level of performance is higher than the lower limit is called a High Performance State. We define the Total High Performance Time as the total time that the system spends operating in High Performance States. Moreover, this paper explains how to utilize the Total High Performance Time in system design. We model a method of controlling a system in pending states by using Extended Stochastic Petri Nets and obtain the characteristics necessary for evaluating the Total High Performance Time by analyzing the model. This approach is applied to a storage system that controls mirrored disks, and shown to be helpful for designing a method of controlling a system in pending states, which has been considered difficult because of the trade-off between performance and reliability.