1. A method of managing an accelerator cache by a storage processor in a data storage system, the method comprising: detecting presence of an accelerator cache storage device in the data storage system; using a first portion of storage space from the detected accelerator cache storage device for an accelerator cache; using a second portion of storage space from the detected accelerator cache storage device for a physical storage tier, wherein the detected accelerator cache storage device is used for both the accelerator cache and the physical storage tier; determining that additional storage space is needed in the physical storage tier; removing storage space from the accelerator cache; and adding the storage space removed from the accelerator cache to the physical storage tier to increase the size of the physical storage tier.