Daisy: Virtual-disk hierarchical storage manager

Abstract

Hierarchical storage managers (HSMs) which automatically migrate infrequently used files from disk drives to lower cost media such as tapes are available from a number of vendors such as IBM [1][4] and Palindrome [5]. Such HSMs require intimate knowledge of file systems and are unable to work adequately with database managers, which often bypass file systems and store their data on raw volumes. In this paper, we describe a virtual-disk HSM which migrates blocks of storage between disk and lower cost media. We designed, implemented and measured the performance of such a virtual-disk HSM in our Daisy project. The virtual-disk approach shares many attributes of virtual memory. Virtual-disk HSM appears to work well for large databases where much of the data is rarely referenced: large amounts of data can be kept on-line with no changes to database managers or applications.