Description
The current trend of computer system technology is towards cpus with rapidly increasing processing power and towards 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 system.
The solution to this problem 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% to 90%) fraction of all I/O requests are captured by a cache of reasonable (e.g. 8 Mbyte) size. 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. We find that disk cache is a powerful means of extending the performance limits of high end computer systems.