Emulating 3490-type virtual volumes

The virtual tape server (VTS) system in a 3494 or 3584 ATLDS uses virtual volumes for all interactions with host software. When these virtual volumes and the data associated with them are being used by the host system, they are stored in the tape volume cache, not on a physical tape device or volume. For more information on tape volume cache, see Tape volume cache and see IBM TotalStorage Enterprise Automated Tape Library (3494) Introduction and Planning Guide. These virtual volumes emulate the functional characteristics of a cartridge system tape. Each virtual volume has the following attributes:

Has a unique volume serial number
Is loaded and unloaded on a virtual device
Supports an IBM Standard Label
Can be appended to after having been initially written from the beginning of the tape
Has an advantage over a physical volume because the mount response time for a virtual volume request, specific (when in cache) or nonspecific, is faster, since there is no dependency on the physical movement of a cartridge or the loading delays of a physical drive

The tape volume cache of the virtual tape server enables the utilization of the 3590 and 3592 tape technology. When a virtual volume is copied from the tape volume cache to a native cartridge, the volume then becomes a logical volume. A native cartridge that contains logical volumes is referred to as a stacked volume. The VTS stacks multiple host-created volumes onto a native cartridge to create a stacked volume. The native library volumes used for stacking are identified through their volume serial numbers.

When a native cartridge identified as a stacked volume is inserted into a library, it becomes part of the volumes managed by the VTS and is not reported to the host as a newly inserted volume. Only the logical volumes specified at the library manager console are reported to the host. By buffering host created volumes, then later stacking them on a native cartridge, the cartridge capacity of the native technology is fully utilized. The cartridges used with this volume stacking technology emulate Cartridge System Tape or Enhanced Capacity Cartridge System Tape to the host system. When a logical volume is moved from a native cartridge to the tape volume cache, the volume becomes a virtual volume again.