Caching is an important feature of ISA Server 2004 and, if configured correctly, caching can provide benefits in speed of response and in reduction of bandwidth usage. At the same time, ISA Server caching there are also situations in which you may need to troubleshoot caching on ISA Server. Use the following guidelines when troubleshooting ISA Server caching:
1- If users are accessing the Internet to retrieve objects rather than retrieving the objects from the ISA Server cache, check to see if caching is enabled. To do this, check the cache configuration to ensure that a cache drive has been created. And confirm that the client computers are configured to use the ISA Server computer as a Web proxy server.
2- If only some objects are cached and the cache contents are deleted frequently, ensure that the cache drive is large enough. Cached content may be being discarded due to lack of space. You can use Performance Monitor to check the Total URLs Cached and Total Memory URLs Retrieved. A low number could indicate a cache drive that is too small.
3- If some Web sites are not being cached at all and you have caching rules configured,ensure that the caching rule order is correct. Check to see that one rule is not blocking another rule from being evaluated. Rules are evaluated in the order that they are listed in the ISA Server Management interface.
4- If users cannot retrieve content from specific Web sites, check to see if negative caching is enabled. Intermittent network problems may have caused one negative response to be cached, thereby affecting all subsequent users.
5- If users are receiving outdated content from a particular Web site that is included in a cache rule, decrease the TTL for the caching rule.
Guidelines for Troubleshooting Caching
6- If objects are being cached but not returned to clients from the cache, check to see if the cache has become corrupted. Use Performance Monitor to check caching statistics. If Performance Monitor indicates that Web content is being cached, but no content is being retrieved from the cache, you may need to clear the ISA Server cache. You can clear the cache by disabling caching and enabling it again.
