Abstract: A system and method for reducing device wait time in response to a host initiated write operation modifying a data block. The system includes a host computer channel connected to a storage controller which has cache memory and a nonvolatile storage buffer in a first embodiment. An identical system makes up the second embodiment with the exception that there is no nonvolatile storage buffer in the storage controller of the second embodiment. The controller in either embodiment is coupled to a cache storage drawer containing a plurality of DASD devices for implementing a RAID parity data protection scheme, and for permanently storing data. The drawer has nonvolatile cache memory which is used for accepting data destaged from controller cache. In a first embodiment, no commit reply is sent to the controller to indicate that data has been written to DASD. Instead a status information block is created to indicate that the data has been destaged from controller cache but is not committed.

Abstract: An adaptive hierarchical cache management system for improving effective cache hit ratios by eliminating unnecessary duplicate cache entries in two coupled cache memories. When a cached Storage Controller (SC) is coupled to a Cached Storage Drawer (CSD), the hierarchical coupling of the SC cache memory and CSD cache memory unnecessarily duplicates cache entries during normal operation. A Conditional Purge procedure purges duplicate lines from the CSD cache subject to a DASD activity threshold. A Prenotify Intent parameter allows the SC to request restaging of the purged cache entry preparatory to fast write or LRU demotion in the SC cache. The new procedures substantially and transparently improve the combined caching efficiency without significant new hardware or software overhead.

Abstract: Often in DASD subsystems, circumstances can occur which prevent the full transfer of the required data from channel to subsystem during a write operation. The disclosed methods prevents this data from later being read and treated as valid data by the host processor. This is achieved by marking data as invalid within the storage subsystem once it is determined that a channel error has occured. Subsequently, upon reading that data, the host processor can be made aware of the data invalidity and treat the data accordingly. In a second embodiment, invalid data is discarded rather than stored over the previous valid version of the data, before it is ever stored on DASD.

Abstract: A system for prestaging data into a cache to increase the speed data is received from a direct access storage drive (DASD) is utilized within a data processing system. This system utilizes multi-track read operations to prestage tracks into the cache. In so doing, the overhead associated with proceeding from one track to the next is reduced. The system allows for the prestaging of up to a cylinder of tracks per prestage. The prestaging system will also allow internally scheduled operations requiring a physical device to interrupt the prestaging if conditions require this action to maintain subsystem performance.