Electrical computers and digital processing systems: memory – Storage accessing and control – Control technique
Reexamination Certificate
2000-11-28
2003-04-29
Portka, Gary J (Department: 2188)
Electrical computers and digital processing systems: memory
Storage accessing and control
Control technique
C707S793000
Reexamination Certificate
active
06557089
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the copying of data that resides in direct access storage devices (“DASDs”). More particularly, the invention concerns an automated, fault-tolerant method of creating a backup copy of a source DASD volume by first performing an instant virtual copy with source volume identifier (ID) suspended, then creating a non-virtual (physical) backup copy from the instant virtual copy with the source volume ID reintroduced.
2. Description of the Related Art
A number of DASD subsystems are capable of performing “instant virtual copy” operations, also referred to as “fast replicate functions.” Instant virtual copy operations work by modifying metadata such as relationship tables or pointers to treat a source data object as both the original and copy. In response to a host's copy request, the storage subsystem immediately reports creation of the copy without having made any physical copy of the data. Only a “virtual” copy has been created, and the absence of any physical copy is completely unknown to the host.
Later, when the storage system receives updates to the original or copy, the updates are stored separately and cross-referenced to the updated data object only. At this point, the original and copy data objects begin to diverge. The initial benefit is that the virtual copy occurs almost instantaneously, completing much faster than a normal physical copy operation. This frees the host and storage subsystem to perform other tasks. The host or storage subsystem may even proceed to create an actual, physical copy of the original data object during background processing, or at another time.
With such benefits, instant virtual copy has been an important development in modern
DASD subsystems, and a number of different embodiments have surfaced. As one example, International Business Machines Corporation (“IBM”) has developed the “FLASHCOPY” technique, as described in U.S. application Ser. No. 09/347,344, filed on Jul. 2, 1999 and entitled “Method, System, and Program for Maintaining Electronic Data as of a Point-In-Time.” A different example is the “SNAPSHOT” technique disclosed in U.S. Pat. No. 5,410,667 entitled “Data Record Copy System for a Disk Drive Array Data Storage Subsystem,” which issued on Apr. 25, 1995. The foregoing references are hereby incorporated herein by reference.
The instant virtual copy technique was developed, at least in part, to quickly create a duplicate copy of data without interrupting or slowing foreground processes. A natural extension of this function has been the creation of a non-virtual “backup” copy of the source data, to aid in disaster recovery. Under, one such technique, an operation such as “FLASHCOPY” or “SNAPSHOT” operation is used to perform an instant virtual copy operation; this creates a virtual target volume identical to the source volume in all respects, even including the volume ID of the source volume. Then, the target volume is taken off-line, which may occur automatically as a result of the instant virtual copy operation or manually at the direction of a system administrator. This is necessary because most systems do not allow multiple volumes with the same volume ID, in order to prevent confusion in uniquely identifying each data volume. After being taken off-line, the (virtual) target volume is used as a source to create a physical backup copy on tape. This may be achieved, for example, using an operation such as a BACKUP, DUMP, etc.
Although the foregoing technique is useful in some respects, there are still certain limitations. Namely, if the system fails prior to taking the (virtual) target volume off-line, confusion can result when the system is brought on-line because there will be two volumes with the same volume ID. Furthermore, if the source volume received any updates prior to system failure, there is a danger of losing these updates if the target volume is incorrectly taken to be the source volume.
A different approach has been developed to avoid the confusion of having both source and target volumes with the same volume ID. In this approach, an operator manually issues an instant virtual copy command with an associated command parameter that causes the system to create a target volume (instant) with a volume ID that differs from its source volume counterpart. This may be achieved, for example, using a “FLASHCOPY” command including a “NO VOLID” parameter. This creates an instant virtual copy of the source volume, but with a different volume ID. Next, the operator manually issues another command causing the storage system to create a physical backup copy of the “target” instant virtual copy. This may be achieved, for example, by using a appropriate command such as BACKUP, DUMP, etc. This creates a non-virtual (physical) backup volume that is identical to the source volume, except for having a different volume ID.
This presents some difficulties if the source volume fails and the backup volume is needed to restore the contents of the source. Namely, since the backup volume's volume ID does not match that of the failed source volume, a recovered backup volume would not be accessible to applications that expect the volume ID of the failed source volume, and the intended function of the restore operation would be defeated. Consequently, restoration of the backup volume requires the operator to perform the added manual operation of changing the recovered volume's volume ID to match that of the failed source volume. This may be done, for example, using the ICKDSF utility provided by the IBM DFSMShsm product. Alternatively, the backup volume's ID may be changed first, and then the volume restoration completed.
Although the foregoing technique is useful in some respects, there are still certain limitations. For one, success of this process requires certain operator input to occur at certain times. As with any process involving humans, the process incurs some risk of error merely because of the human factor. In addition, there are greater labor costs because of the need for human involvement rather than utilizing automated processes. Furthermore, the marketplace demands increasingly competitive, automated solutions to problems such as these.
For the foregoing reasons, then, known backup processes based on the instant virtual copy are not completely adequate for some applications due to certain unsolved problems.
SUMMARY OF THE INVENTION
Broadly, the present invention concerns an automated, fault-tolerant method of creating a physical backup copy of a source DASD volume by first performing an instant virtual copy with source volume ID suspended, then creating a non-virtual (physical) backup copy from the instant virtual copy with the source volume ID reintroduced.
According to the invention, the instant virtual copy may be performed using similar principles as a FLASHCOPY operation with the NO COPY VOLID option selected. This creates a virtual duplicate of the source volume on the DASD, minus the source's volume ID. Advantageously, novel operations are added to provide the virtual target volume with a hidden representation of the source volume ID. Next, the target volume is used as source for a physical copy operation to magnetic tape or other backup media. Importantly, this copy operation utilizes the hidden representation of the source volume ID to reintroduce the source's volume ID into the backup copy. The resultant backup copy on tape is an exact duplicate of the source volume. After completing the physical backup copy, the instant virtual copy is deleted by freeing data storage allotted to the instant virtual copy for use in other storage purposes. In the case of Home Area Architecture systems, deletion of the instant virtual copy may, for example, be performed using a WITHDRAW FLASH COPY RELATIONSHIP operation.
The foregoing features may be implemented in a number of different forms. For example, the invention may be implemented to provide a method of automated backup using a volume ID-suppressed instant virtual copy
Reed David Charles
Thompson John Glenn
Dan Hubert & Assoc.
International Business Machines - Corporation
Portka Gary J
LandOfFree
Backup by ID-suppressed instant virtual copy then physical... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Backup by ID-suppressed instant virtual copy then physical..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Backup by ID-suppressed instant virtual copy then physical... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3023659