In a storage system including a write-back cache, dirty data can be flushed from the cache while a controller continues to service host I/O requests. A controller is capable of flushing all the dirty data in the cache to a storage device in response to an indication to do so, such as an indication of impending failure. The controller is further capable of responding to I/O requests from the host during the flushing of the dirty data. In particular, the controller is capable of responding to write requests from the host system by storing data on the storage device during the flushing of the dirty data.