The simplest way to judge the effectiveness of the cache is to examine the percentage of cache hits, that is, how often data sought in the cache is found there. Cache misses, however, are even more important. When data is not found in the cache, or elsewhere in memory, the file system must make a time-consuming search of the disk. An application with a miss rate of 10% (a hit rate of 90%) requires twice as much disk I/O as an application with a miss rate of 5%.
Also, especially on a workstation, you must keep cache rates in perspective. On a system where cache reads are minimal, the hit-and-miss rates are not a significant performance factor. However, when running I/O-intensive applications such as databases, the cache hit-and-miss rates are an important performance measure of the computer and the application.