1. Field
Implementations of the invention relate to application transparent autonomic availability on a Storage Area Network (SAN) aware file system.
2. Description of the Related Art
Computing systems often include one or more host computers (“hosts”) for processing data and running application programs, direct access storage devices (DASDs) for storing data, and a storage controller for controlling the transfer of data between the hosts and the DASD. Storage controllers, also referred to as control units or storage directors, manage access to a storage space comprised of numerous hard disk drives, otherwise referred to as a Direct Access Storage Device (DASD). Hosts may communicate Input/Output (I/O) requests to the storage space through the storage controller.
Storage controllers may provide copy services. With the copy services, data on one storage device, such as a DASD, may be copied to the same or another storage device so that access to data volumes can be provided from two different devices or to have a backup copy.
International Business Machines Corporation (IBM), the assignee of the subject patent application, provides remote copy services for maintaining remote copies of data at a secondary storage device, including extended remote copy (XRC) and peer-to-peer remote copy (PPRC). These systems provide techniques for recovering data updates between a last, safe backup and a system failure. Such data shadowing systems can also provide an additional remote copy for non-recovery purposes, such as local access at a remote site.
Another example of a copy service is a point-in-time copy, which involves physically copying all the data from source volumes to target volumes so that the target volume has a copy of the data as of a point-in-time. A point-in-time copy can also be made by logically making a copy of the data and then only copying data over when necessary, in effect deferring the physical copying, and this is referred to as an “instant virtual copy” operation or “fast replicate function.”
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 an additional physical copy is completely unknown to the host. 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.
One such instant virtual copy operation is known as a FlashCopy® operation. Further details of the FlashCopy® operations are described in the commonly assigned U.S. Pat. No. 6,661,901, issued on Aug. 26, 2003, entitled “Method, System, and Program for Maintaining Electronic Data as of a Point-in-Time”, which patent application is incorporated herein by reference in its entirety.
Typically, backup of a file via a copy services operation provided by a storage controller is non-disruptive to a host computer. However, the process of recovering a file (i.e., copying the file from a backup copy to the original (“source”) copy) may be disruptive. The host computer needs to know of and maintain the location of where the data is being copied. This becomes especially difficult when using block based copy services, which copy portions of a volume rather than an entire volume of data. If the host computer knows where all of the backup copies are, recovery of a file or Logical Unit Number (LUN) is still a manually intensive procedure. A LUN may be described as a unique number that may identify a specific disk and is typically used to refer to a disk having that LUN.
Also, currently, when a storage controller fails, a file system at a host computer uses copy services to migrate data. However, this is not an efficient process.
Therefore, there is a continued need in the art for improved file access and migration.
USPTO Backgrounds
USPTO Backgrounds