Dasd I/O caching method and application including replacement policy minimizing data retrieval and storage costs
AssigneeInternational Business Machines Corporation
InventorsRobert Allen Rose, Joseph Harry Nord
Life of this patent
Estimating the term…
Abstract
The performance of a DASD having a data cache and at least one set of R/W heads is improved by implementing a replacement policy which, upon determining that a request for data in the DASD requires replacement of a data in a data cache buffer, selects cache data corresponding to data which is cheapest to retrieve from the DASD in view of a location of the DASD R/W heads and replaces the selected cache data with the requested data, thus keeping the cache filled with data which is least expensive to retrieve from the DASD. Data in the DASD is updated from the cache when it is inexpensive.
Claims20
A method in a data processing system for improving performance of a DASD having a data cache and at least one set of R/W heads, comprising:
- receiving a request for data in said DASD requiring replacement of data in a data cache buffer;
- in response to receiving said request, selecting cache data corresponding to data which is cheapest to retrieve from said DASD in view of a location of said at least one set of R/W heads, wherein near clean data is selected over far clean data, far clean data is selected over near dirty data, and near dirty data is selected over far dirty data;
- and
- replacing said selected cache data with said requested data, wherein data within said cache selected for replacement is least expensive to retrieve from said DASD at the time of said request.
A data processing system for improving performance of a DASD having a data cache and at least one set of R/W heads, comprising:
- means for receiving a request for data in said DASD requiring replacement of data in a data cache buffer;
- means for selecting cache data corresponding to data which is cheapest to retrieve from said DASD in view of a location of said at least one set of R/W heads, wherein near clean data is selected over far clean data, far clean data is selected over near dirty data, and near dirty data is selected over far dirty data;
- and
- means for replacing said selected cache data with said requested data, wherein data within said cache selected for replacement is least expensive to retrieve from said DASD at the time of said request.
A storage device readable by a data processing system and encoding executable instructions for the data processing system, comprising:
- means for receiving a request for data in said DASD requiring replacement of data in a data cache buffer;
- means for selecting cache data corresponding to data which is cheapest to retrieve from said DASD in view of a location of said at least one set of R/W heads, wherein near clean data is selected over far clean data, far clean data is selected over near dirty data, and near dirty data is selected over far dirty data;
- and
- means for replacing said selected cache data with said requested data, wherein data within said cache selected for replacement is least expensive to retrieve from said DASD at the time of said request.
Dependencies are inferred from the claim text.