Error detection/correction and fault detection/recovery – Data processing system error or fault handling – Reliability and availability
Reissue Patent
1995-08-31
2001-01-30
De Cady, Albert (Department: 2784)
Error detection/correction and fault detection/recovery
Data processing system error or fault handling
Reliability and availability
C707S793000
Reissue Patent
active
RE037038
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates in general to methods and systems for maintaining continued availability of datasets in external storage associated with data processing systems, and in particular to backup copying of records in external storage concurrent with a dramatically shortened suspension of data processing system application execution occasioned by such copying. Still more particularly, the present invention relates to automatic termination or resumption of backup copy sessions in a backup copy process.
2. Description of the Related Art
A modern data processing system must be prepared to recover, not only from corruptions of stored data which occur as a result of noise bursts, software bugs, media defects, and write path errors, but also from global events, such as data processing system power failure. The most common technique of ensuring the continued availability of data within a data processing system is to create one or more copies of selected datasets within a data processing system and store those copies in a nonvolatile environment. This so-called “backup” process occurs within state-of-the-art external storage systems in modern data processing systems.
Backup policies are implemented as a matter of scheduling. Backup policies have a space and time dimension which is exemplified by a range of datasets and by the frequency of backup occurrence. A FULL backup requires the backup of an entire range of a dataset, whether individual portions of that dataset have been updated or not. An INCREMENTAL backup copies only that portion of the dataset which has been updated since a previous backup, either full or incremental. The backup copy thus created represents a consistent view of the data within the dataset as of the time the copy was created.
Of course, those skilled in the art will appreciate that as a result of the process described above, the higher the backup frequency, the more accurately the backup copy will mirror the current state of data within a dataset. In view of the large volumes of data maintained within a typical state-of-the-art data processing system backing up that data is not a trivial operation. Thus, the opportunity cost of backing up data within a dataset may be quite high on a large multiprocessing, multiprogramming facility, relative to other types of processing.
Applications executed within a central processing system are in either a batch (streamed) or interactive (transactional) mode. In a batch mode, usually one application is executed at a time without interruption. Interactive mode is characterized by interrupt driven multiplicity of applications or transactions.
When a data processing system is in the process of backing up data in a batch mode system, each process, task or application within the data processing system is affected. That is, the processes supporting the batch mode operations are suspended for the duration of the copying. Those skilled in the art will recognize that this event is typically referred to as the “backup window.” In contrast to batch mode operations, log based or transaction management applications are processed in the interactive mode. Such transaction management applications eliminate the “backup window” by concurrently updating an on-line dataset and logging the change. However, this type of backup copying results in a consistency described as “fuzzy.” That is, the backup copy is not a precise “snapshot” of the state of a dataset/database at a single point in time. Rather, a log comprises an event file requiring further processing against the database.
A co-pending U.S. patent application Ser. No. 07/385,647, filed Jul. 25, 1989, entitled A Computer Based Method for Dataset Copying Using An Incremental Backup Policy, illustrates backup in a batch mode system utilizing a modified incremental policy. A modified incremental policy copies only new data or data updates since the last backup. It should be noted that execution of applications within the data processing system are suspended during copying in this system.
As described above, to establish a prior point of consistency in a log based system, it is necessary to “repeat history” by replaying the log from the last check point over the datasets or database of interest. The distinction between batch mode and log based backup is that the backup copy is consistent and speaks as of the time of its last recordation, whereas the log and database mode require further processing in the event of a fault in order to exhibit a point in time consistency.
U.S. Pat. No. 4,507,751, Gawlick et al., entitled Method and Apparatus For Logging Journal Data Using A Write Ahead Dataset, issued Mar. 25, 1985, exemplifies a transaction management system wherein all transactions are recorded on a log on a write-ahead dataset basis. As described within this patent, a unit of work is first recorded on the backup medium (log) and then written to its external storage address.
Co-pending U.S. patent application Ser. No. 07/524,206, filed May 16, 1990, entitled Method and Apparatus for Executing Critical Disk Access Commands, teaches the performance of media maintenance on selected portions of a tracked cyclic operable magnetic media concurrent with active access to other portions of the storage media. The method described therein requires the phased movement of customer data between a target track to an alternate track, diversion of all concurrent access request to the alternate track or tracks and the completion of maintenance and copy back from the alternate to the target track.
Requests and interrupts which occur prior to executing track-to-track customer data movement result in the restarting of the process. Otherwise, request and interrupts occurring during execution of the data movement view a DEVICE BUSY state. This typically causes a re-queuing of the request.
It should therefore be apparent that a need exists for a method and system whereby the maximum availability of application execution within a data processing system is maintained while creating backup copies which exhibit a consistent view of data within an associated database, as of a specific time. Additionally, a need exists for automatically terminating or resuming backup copy sessions upon an abnormal interrupt in the backup copy process.
SUMMARY OF THE INVENTION
It is therefore one object of the present invention to provide an improved method and system for backup copying of records in external storage concurrent with a dramatically shortened suspension of data processing system application execution occasioned by such copying.
It is another object of the present invention to provide a method and system for automatically terminating a backup copy session after an abnormal interrupt in the backup copy process.
It is yet another object of the present invention to provide a method and system for automatically determining the status of a backup copy session and selectively resuming or terminating a backup copy session after a reset notification is generated during the backup copy process.
The foregoing objects are achieved as is now described. A status indication is entered into activity tables associated with a plurality of storage subsystems and devices within a data processing system in response to initiation of a backup copy session. Status indications are then entered upon successful completion of a backup copy session within the data processing system. The indications within the activity tables are reviewed to determine the status of a backup copy session upon restarting a resource manager, abnormal termination of a backup copy program, or an operating system initial program load. If a backup copy session has been initiated but not completed, the backup copy session is then terminated. The indications within the activity tables are also reviewed and checked against a storage subsystem to determine the status of a backup copy session if a reset notification is raised by a storage subsystem. The tracks extents which are active for a volume associated with a particular ses
Eastridge Lawrence E.
Kern Robert Frederic
Micka William Frank
Mikkelsen Claus William
Ratliff James Mitchell
Cady Albert De
Felsman Bradley Vaden Gunter & Dillon, LLP
International Business Machines - Corporation
Schecter Manny W.
Ton David
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