Data processing: database and file management or data structures – Database design – Data structure types
Reexamination Certificate
1998-01-13
2001-04-03
Von Buhr, Maria N. (Department: 2771)
Data processing: database and file management or data structures
Database design
Data structure types
Reexamination Certificate
active
06212531
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to improvements in the field of computer systems having backup/restore or archive/retrieve subsystems, and more particularly, to a method for implementing point-in-time copy operations using snapshot functions.
2. Description of Related Art
In a data processing system, a backup/restore subsystem is typically used to save a recent copy or version of one or more data sets or portion thereof on some form of backup data storage device, such as magnetic or optical disk drives, tape drives, or other memory. The backup/restore subsystem is used to protect against loss of data. For example, if an on-line version of one or more data sets is destroyed, corrupted, deleted, or changed because of power failure, hardware, or software error, user error or some other type of problem, the latest version of those data sets which are stored in a backup/restore subsystem can be restored and therefore the risk of loss of data is minimized. It is readily apparent that backup/restore subsystems are and will remain an important part of the field of data processing.
Successful recovery of data to a known consistent state requires a backup of all components of the data at the same consistent point in time. Generally, a point in time backup is a copy of the data which is logically consistent to a given point in time, with the: restriction that the amount of time to obtain logical consistency is significantly less than the amount of time to actually copy the data.
Concurrent copy, also known as time-zero copy, provides the ability to create a point-in-time backup. Concurrent copy is a point in time backup which uses a combination software and microcode architecture to obtain a copy of the original data at the time the backup was initiated. However, concurrent copy is usually only supported for data residing on storage subsystems which implement the concurrent copy functions.
One storage subsystem that does not support concurrent copy functions is the log-structured array subsystem (LSA). An LSA subsystem implements “virtual volumes”, wherein each virtual volume is created using a “virtual track table” having pointers to “virtual tracks” (i.e., records) in a sequential byte stream, wherein updated tracks are written to a new location at the logical end of the byte stream and their associated pointers, are reset to the new locations. Thereafter, the tracks at the old location in the sequential byte stream are no longer needed and can be released as free space for reclamation and reuse.
In certain products, emulation functions performed by the LSA subsystem permit computer programs executed by a host processor coupled to the LSA subsystem to “view” the LSA subsystem as a standard direct access storage device (DASD) with sequentially numbered tracks. However, such emulation does not necessarily extend to all functions generally capable of being supported with standard DASD.
Currently available LSA subsystems do support a very fast copy function called a snapshot function, which operates by copying pointers between virtual track tables representing different virtual data volumes without actually moving any data. On the other hand, the snapshot function suffers from a restriction that the source and target locations must be within the subsystem, and the same device types. As a result, a straightforward backup copy using current snapshot functions does not achieve point-in-time backup on LSA subsystems.
Thus, there is a need in the art for methods for providing point in time backups on LSA subsystems, wherein the point-in-time backups use snapshot functions.
SUMMARY OF THE INVENTION
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method, apparatus, and article of manufacture for performing a point-in-time backup using a snapshot function. Work space on a work virtual volume is obtained to hold the snapshot copy of the source data being copied from a source virtual volume. Updates to the source virtual volume are suspended during the snapshot function, so as to provide a logically consistent view of the source virtual volume at a common point in time. Pointers are copied from a virtual track table of the source virtual volume to a virtual track table of the work virtual volume without actually moving any data on data storage devices referenced by those pointers. As a result, the snapshot function provides a method for copying the source virtual volume to the work virtual volume very quickly. Upon completion of the snapshot function, updates to the source virtual volume may be resumed. Subsequently, a backup is performed in the usual manner, except that the backup retrieves the source data from the work virtual volume rather than the source virtual volume.
One object of the present invention is that it the point-in-time backup using the snapshot function may be performed on multiple subsystems or target data storage devices that are different from the source data storage device.
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Blea David Randall
Blea Donald Reynold
Haye Mark Alan
Kern Ronald Maynard
Shackelford David M.
International Business Machines - Corporation
Konrad Raynes & Victor
Victor David W.
Von Buhr Maria N.
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