Abstract

The present data file storage management system for snapshot copy operations maintains a two level mapping table which enables the data files to be copied using the snapshot copy process and only having to update a single corresponding mapping table entry when the physical location of the data file is changed. The snapshot copy updates to the contents of the first level of the two level mapping table are stored on the backend data storage devices to provide a record of the snapshot copy operation which can be used to recover the correct contents of the mapping table. This record of the snapshot copy operations remains valid even though the physical location of a copied data file instance is subsequently changed. Furthermore, the physical storage space holding the updated portions of the first level of the two level mapping table can be managed using techniques like those used to manage the physical storage space holding data file instances. Mapping table updates resulting from the snapshot copy operation are delayed until all mapping table updates resulting from earlier data file write operations have been completed and any attempt to update the mapping table to reflect data written to the original data file or the copy data file that occurs after initiation of the copy must wait until the first set of mapping table pointers have been copied.

Other References

• Ritchie, Dennis M.: Ken Thompson; The UNIX Time-Sharing System, Association for Computing Machinery, Inc., pp. 1-8, 1974
• Leffler, Samuel J.; Marshall Kirk McKusick; Michael J. Karels; John S. Quarterman; The Design and Implementation of the 4.3BSD UNIX Operating System, Addison-Wesley Publishing Company; 1989; pp. 187-20