A cache on-demand module employing a cache performance module for managing size adjustments to a cache size of a cache memory in view of supporting an optimal performance of a storage subsystem employing the cache memory by determining an optimal cache size of the cache memory for supporting the optimal performance of the storage subsystem, and reporting any size adjustment to the cache size of the cache memory based on the determined optimal cache size of the cache memory. The cache on-demand module further employs a cache accounting module for managing a client expense account associated with the cache memory by determining whether a client charge or a client rebate is warranted as a function of any size adjustment to the cache size of the cache memory by the cache performance module.