The device partitions used for disk caching need to be dedicated to the cache; that is, do not use these physical disks to contain any other file systems, and do not use them for any purpose other than storing the proxy cache. Additionally, do not use data compression on any disk used for the proxy cache because it reduces performance.
Each cache storage device (whether a disk or a file) incurs memory overhead on the proxy server. In general, using an entire physical disk as a single cache device yields the best performance. Using RAID or other mechanisms to combine multiple physical disks into a single logical disk can be counterproductive. If you want to use multiple disks, specify them as multiple cache devices by using the Cache Settings configuration form or by editing the CacheDev directive in the proxy configuration file. This method allows the proxy server to control the parallelism of reading and writing to multiple disks, and does not rely on the performance of the operating system or a disk subsystem.