Point-in-time copying of virtual storage

#The present invention relates to computer systems, and more specifically, to methods and systems of increasing computer system availability.

#Computer systems often include a control application program that runs, in association with other application programs, in order to monitor data indicative of system operation. In the event of an error, the control application typically issues a command to take a snapshot image of the computer system's working memory, which is often used for subsequent error diagnosis, debugging and error prevention. However, the taking of the snapshot image often places the computer system in a non-dispatchable state, in which the application programs cannot run properly and time-outs may occur.

#According to one embodiment of the present invention, a computer-implemented method for increasing computer system availability, the method includes making in a real storage, via a computer processor, a point-in-time copy of a first page content stored in a first page data structure by creating a second page content in a second data structure, the second page content pointing to actual data pointed to by the first page content, the first page content includes a location of a virtual page in a first virtual storage, storing the second page content in the second data structure, the first page data structure and the second page data structure being stored in the real storage, marking the first page content in the first page data structure with a point-in-time page protection bit, wherein the point-in-time page protection bit prevents a modification of the virtual page, in response to an attempt to modify the virtual page, copying the virtual page in the event the first page content in the first page data structure is marked with the point-in-time page protection bit, storing the copied virtual page in a second virtual storage, at least some of the second virtual storage is stored in the real storage, and altering the second page content in the second data structure to point to the stored virtual page, the second page content includes a location of the stored virtual page in the second virtual storage.

#The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

#FIG. 1 illustrates a schematic diagram of an embodiment of a computing environment for use with an embodiment of the present invention;

#FIG. 2 illustrates a flowchart of an embodiment of a method of performing instant virtual copying of virtual storage;

#While the description below describes the present invention with respect to mainframes, the present invention is not limited to mainframes. Rather, the present invention can be used in other computing environments as are known in the art.

#Instant virtual copy (IVC) technology allows creation of point-in-time (PIT), full volume copies of data, with both the source and target IVC copies immediately available for read or write access. IVC technology works by creating a copy of a source volume on a target volume. The target volume copy is referred to herein as an IVC copy. IVC copies are typically used to create PIT copies of a source volume, i.e., the target volume represents a copy of the source volume, as it existed at some PIT.

#When an IVC operation is initiated, a copy relationship is created between a source volume and target volume. An IVC relationship is a “mapping” of the PIT copy target volume to the PIT copy source volume. One example of this mapping is a bitmap representing the tracks on a target volume and a pointer to the source volume. When an IVC copy is made, the relationship between the target volume and the source volume is established via the pointer from the source volume to the target volume and a bitmap is created, which indicates which tracks on the target volume actually reside on the target volume. Thus, when data is requested from the target volume, the storage controller (or a storage unit) checks to see if the data is an IVC of another volume, by checking the pointer, and before reading the requested track, the storage controller checks the bitmap to determine whether the storage controller should read the data from the target volume, or if the requested data still resides on the source volume. Hence, a copy can be made by establishing the pointer to the source volume and clearing the bitmap, which indicates that all tracks on the target volume actually reside on the source volume. Thus, when the source volume is updated, a copy of the track is created on the target volume before the update is made, the corresponding bit in the bitmap on the target volume is turned on and the updated track is written to the source volume, so that subsequent requests to read that track from the target volume will cause the storage controller to now read the track from the target volume. This mapping allows an instant virtual point-in-time copy of that source volume to be copied to the associated target volume.