Abstract: Disclosed methods and systems relate to characterizing a dynamic performance quality of service available from a storage element within a storage system. An exemplary method includes initiating a known I/O request to the storage element; measuring a time the storage element takes to respond to the known I/O request; and reporting a measure of the quality of service available from the storage element. One implementation of the method further includes using the time measurement and an estimation algorithm to calculate the quality of service and adjusting the load on the storage element based on the quality of service.

Abstract: 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.