1. Field of the Invention
The present invention relates to a method, system, and an article of manufacture for borrowing physical volumes.
2. Description of the Related Art
In prior art virtual tape storage systems, hard disk drive storage emulates tape drives and tape cartridges. For instance, host systems perform input/output (I/O) operations with respect to a tape library by performing I/O operations with respect to a set of hard disk drives that emulate the tape library. In prior art virtual tape storage systems, such as the International Business Machines (IBM) Magstar** Virtual Tape Server, at least one virtual tape server (VTS) is coupled to a tape library comprising numerous tape drives and tape cartridges. The VTS is also coupled to a direct access storage device (DASD), comprised of numerous interconnected hard disk drives.
The DASD functions as a cache to volumes in the tape library. In VTS operations, the VTS processes the host's requests to access a volume in the tape library and returns data for such requests, if possible, from the cache. If the volume is not in the cache, then the VTS recalls the volume from the tape library to the cache, i.e., the VTS transfers data from the tape library to the cache. The VTS can respond to host requests for volumes that are present in the cache substantially faster than requests for volumes that have to be recalled from the tape library to the cache. However, since the capacity of the cache is relatively small when compared to the capacity of the tape library, not all volumes can be kept in the cache. Hence, the VTS also premigrates volumes from the cache to the tape library, i.e., the VTS transfers data from the cache to the tape cartridges in the tape library.
The tape library may comprise a plurality of storage pools. Each storage pool may comprise of zero, one or a plurality of tape cartridges. Requests from a host may identify a storage pool into which particular data should be written into.
Notwithstanding the use of storage pools in a virtual tape library, there is a need in the art for improved techniques for managing storage pools in virtual tape library systems.