Performance of an I/O Channel with Multiple Paging Drums. (Digest Edition)

摘要

For rotating storage units, a paging drum organization is known to offer substantially better response time to I/O requests than is a more conventional (file) organization. When several, asynchronous paging drums are attached to a single I/O channel, however, much of the gain in response time due to the paging organization is lost; this article investigates the reasons for this loss in performance. A model of an I/O channel with multiple paging drums is presented and a Markov chain that closely approximates the behavior of the I/O channel is embedded into the model. The analysis then leads to the moment generating function of sector queue size and the Laplace-Stieltjes transform of the waiting time. A significant observation is that the expected waiting time for an I/O request to a drum can be divided into two terms: one independent of the load of I/O request to the drum and another that monotonically increases with increasing load. (Modified author abstract)