Optimal file management in a hybrid storage system

In this paper the authors analyze a hybrid storate system for data management which combines conventional magnetic disks and write-once, read-many optical disks (ODs) which offer high-density low-cost storage capability. Updates of the files stored on the ODs are temporarily stored in differential files on magnetic disks. Periodically, the differential file corresponding to each OD file is copied into free space on the OD to ‘refresh’ that file. After a time interval, the OD files and the most recent differential files are copied onto new optical media; this process is known as file reorganization. Using measures of data file volatility, file sizes, device costs, and costs for refreshing and reorganizing files, the authors show how this problem is similar to deterministic inventory problems and, using this analogy, develop a model which indicates how often files should be refreshed and reorganized.