Disk cache—miss ratio analysis and design considerations

Abstract

The current trend of computer system technology is toward CPUs with rapidly increasing processing power and toward disk drives of rapidly increasing density, but with disk performance increasing very slowly if at all. The implication of these trends is that at some point the processing power of computer systems will be limited by the throughput of the input/output (I/O) system.A solution to this problem, which is described and evaluated in this paper, is disk cache. The idea is to buffer recently used portions of the disk address space in electronic storage. Empirically, it is shown that a large (e.g., 80-90 percent) fraction of all I/O requests are captured by a cache of an 8-Mbyte order-of-magnitude size for our workload sample. This paper considers a number of design parameters for such a cache (called cache disk or disk cache), including those that can be examined experimentally (cache location, cache size, migration algorithms, block sizes, etc.) and others (access time, bandwidth, multipathing, technology, consistency, error recovery, etc.) for which we have no relevant data or experiments. Consideration is given to both caches located in the I/O system, as with the storage controller, and those located in the CPU main memory. Experimental results are based on extensive trace-driven simulations using traces taken from three large IBM or IBMcompatible mainframe data processing installations. We find that disk cache is a powerful means of extending the performance limits of high-end computer systems.

Caching and other disk access avoidance techniques on personal computers

“…These results are at odds with Smith's study of caching on a mainframe [8] where he indicated that large blocking factors greatly reduce caching benefits for sequential files. This experiment is also significant because the percent savings is also steeply increasing for the RAM disk which does not do I/O at all.…”

“…Interestingly, on a PC it makes little sense to have more than one set of buffers for a file because there is no concurrent CPU and I/O possible under DOS. This aspect of disk access avoidance is mentioned because Smith [8] found that file blocking loses some of its performance advantages when caching is in effect.…”

Swap compression: resurrecting old ideas

“…It has already been proved that caching is a good solution to increase the performance of disk operations [8]. In our scenario, a cache for swapped pages should also increase the swapping performance, if a few problems could be solved.…”

Exploring the data locality of on-board disk cache

“…Smith [1] considered a number of design parameters for such a disk cache, including cache location, cache size, replace algorithms, block sizes, access time, bandwidth, consistency, error recovery, etc. Each of these parameters was discussed and/or evaluated in terms of trace driven simulations.…”