Emulating 3490-type virtual tape devices

From a host perspective, the virtual system looks like multiple 3490E control units, each with 16 tape devices. Each emulated device is called a virtual tape device. The virtual system handles all 3490 tape commands. Each virtual device has the following attributes:

Has a host device address
Is included in the I/O generation for the system
Is varied online or offline to a host
Signals ready when a virtual volume is loaded
Responds to and processes all 3490E tape commands
Becomes not ready when a virtual volume is rewound and unloaded
Indicates that it has a cartridge loader
Can be associated with a pool of scratch volumes that allow very fast mount access for scratch mounts
Note: The active status of the cartridge loader depends on the availability of scratch volumes in the assigned pool.

Data is written and read as if it is stored on a real Standard or Enhanced Cartridge System Tape; however, within the system it is really stored on DASD. All tape read and write commands are translated to read and write data records to or from DASD. Volumes residing on the DASD are called virtual volumes. For more information concerning virtual volumes, see Emulating 3490-type virtual volumes.

All host interactions with data in a VTS are through virtual volumes and associated virtual tape devices; there is no direct access to the data on a physical cartridge or device.