Optimization of Mass Storage Hierarchies
Bruce Jacob · 2000
Optimization is often a question of where one should put one’s money in improving performance. As far as large storage hierarchies go, intuition suggests (and common practice supports) adding as much as is affordable of the fastest technology available. Many cache hierarchy studies have shown that this is often not the optimal approach, and we show that for mass storage hierarchies it always tends to be the wrong approach. For large data sets, as is the case for network file servers, a machine with no RAM and several gigabytes of disk performs 30 % faster than a machine with no disk and a cost-equivalent amount of RAM. This paper presents a mathematical analysis of the optimization of an I/O hierarchy, as well as trace driven simulations of a network file server in support of the analysis. Over the past several years, there has been a substantial increase in the speed and capacity demands placed on computer memory systems. Great strides have been made in the capacity of mass storage devices such as magnetic disk, tape, and optical media, but improvements in the speed of these devices has not kept up with the improvements in CPU speeds and semiconductor memory. Caching is used to hide the deficiency, but the widening gap between semiconductor memory and