How do you disable an an Online Recovery Server controller status?

I have a server that the cache ratio is set at 100% read and 0% write. We tried changing this through the ACU with no luck. The only option the ACU offeres is 100% read and 0% write. Further research shows “If the Array Accelerator has been permanently disabled, is not installed, or the controller has not yet been configured, this area is unavailable. In addition, if the controller has been enabled as an Online Recovery Server controller, the ratio is automatically set to the highest percentage of the read-ahead cache.” My question is how can I change this from 100/0 to 75/25?