Proxy: Large Files May Not Be Cached (201184)

SYMPTOMS

After you download a large file using HTTP or FTP through a Microsoft Proxy server, you may find that the file does not exist in any of the subfolders in the Urlcache folder. In this article, a large file would be any file over 1 MB in size.

CAUSE

This problem occurs becaseu by default, the proxy server divides the cache into one directory for every 500 MB of cache size (with a minimum of 5 folders and a maximum of about 200 folders).

When you specify a 1 GB cache, you end up with 5 folders with a size limit of 200 MB each. In addition to the 200 MB size limit, the Proxy server does not store any individual file larger than one-eigth the size of the folder limit, in this case 200 divided by 8 equals 25 MB. The reason this limit exists is because a large file that takes up so much space forces so many other, potentially useful files out of the cache. This is usually counterproductive. For example, it is inefficient to delete 3,000 average sized files, some of which might be frequently used, to store a single 30 MB file that may never be used again.

WORKAROUND

This limit cannot be overridden, but you can work around this limit by increasing the overall cache size. To cache an object of 30 MB, you would need a total cache size of 1,200 MB (1,200 MB divided by 5 MB, and then divided again by 8 MB equals 30 MB).