If the file cache is not utilized, your server is not performing optimally. Since most sites have lots of GIF or JPEG files that are intended to always be cacheable, you need to use your cache effectively.
Some sites, however, do almost everything through CGIs, SHTML, or other dynamic sources. Dynamic content is generally not cacheable, and inherently yields a low cache hit rate. Don’t be alarmed if your site has a low cache hit rate. The most important thing is that your response time is low. You can have a very low cache hit rate and still have very good response time. As long as your response time is good, it is less important that the cache hit rate is low.
Check your hit ratio using statistics from perfdump, the Admin Console Monitoring tab, or wadm stats commands. The hit ratio is the percentage of times the cache was used with all hits to your server. A good cache hit rate is anything above 50%. Some sites can even achieve 98% or higher. For more information, see File Cache Statistics Information.