The proxy server can store the cache on a physical storage device or in system memory. The type of cache storage that is better for your system depends on the capabilities of your hardware and on whether it is more important to have fast cache response or to have a larger number of items stored in the cache. Response time for a memory cache typically is faster than for a disk cache, but the size of a memory cache is limited by the amount of RAM in the proxy server machine. The size of a disk cache is limited by the size of the storage device, which typically is much larger than the amount of RAM.
For disk caches, Caching Proxy uses raw disk caching, which means that the proxy server writes directly to the cache device without using the operating system's read and write protocols. The storage device for a disk cache must be prepared by using the htcformat command. Details about htcformat are included in the section Configuring basic caching.