We present a model for data reorganization in parallel disk systems that is geared toward load balancing in an environment with periodic access patterns. Data reorganization is performed by disk cooling, i.e., migrating files or extents from the hottest disks to the coldest ones. We develop an approximate queueing model for determining the effective arrival rates of cooling requests and discuss its use in assessing the costs versus benefits of cooling actions.

An exact solution for the performance analysis of a typical single-bus multiprocessor system is presented. The multiprocessor system is modeled by a Markovian queueing network. An r-stage hypoexponential distribution or an r-stage hyperexponential distribution is used to represent the nonexponential service times. Consequently, the equilibrium probabilities of two-dimensional Markov chains are expressed by simple recurrence relations. Processing efficiency is used as the primary measure of performance. To investigate the effects of different service time distributions on system performance, comparative results are obtained for a large set of input parameters. The numerical results illustrate that processing efficiency attains its maximum value for a constant (deterministic) service time; if service time of common memory is hypoexponentially distributed, then approximating the service time by an exponential distribution produces less than 6% error on the system performance.>

A closed-form solution for the performance analysis of multiple-bus multiprocessor systems is presented. A Markovian queueing network model has been developed to investigate the effects of memory and bus contentions on the system performance. The symmetrical structure of the Markov chains of the queueing model makes it possible to demonstrate that the local balance is satisfied. Consequently, the probabilities of the states of Markov chains can be expressed by simple formulas. Processing efficiency is used as a performance measure. However, this method is easily extendable to other performance measures. To investigate the effects of the system design parameters on the multiprocessor system performance, comparative results have been obtained for a large family of multiprocessor configurations from unibus to bus-sufficient systems.