A virtual tape link (VTL) is a virtual tape file which works as a unidirectional data transfer conduit rather than as a physical file. A VTL establishes this conduit (or pipe) between two logical tape units (LTUs) located on one or more mvBase Servers. One LTU functions as a write (send) device, and the other LTU functions as a read (receive) device.
VTLs can be predefined in the Administration Utility or dynamically defined using the SET-TAPEFILE TCL command. This allows VTLs to be used as an ad hoc data transfer and backup mechanism between various mvBase Servers. It is not necessary to take these servers out of service for reconfiguration when transferring data. Thus, the system administrator has the ability to create and delete VTLs while a system is running and gains considerable flexibility in backup processes.
VTLs have specific file names which can be accessed by processes on different systems on the network. VTLs can be opened, read, written to, saved and closed using file names and standard file system commands.
Once the VTL is configured, it can be selected, attached and used with paired and compatible tape commands or functions. The Transferring Data via a Virtual Tape Link procedure contains more information about suitable command pairs.
The process of implementing VTLs can be broken into three specific stages which, combined with certain restrictions and considerations, comprise other related topics. See Using mvBase Tape Units for additional information.
Considerations
Currently, VTLs can be configured via the Administration Utility or at the TCL prompt via SET-TAPEFILE. There are three options:
If you define the VTL in the Server tab of the Administration Utility, the VTL is preserved when you shut down and restart the Server system.
If you define the VTL at the TCL prompt and do not include this as part of the USER-COLD-START Proc, the VTL is lost every time you shut down the Server system.
If you define the VTL at the TCL prompt and do include this as part of the USER-COLD-START Proc, the VTL is retained when you shut down and restart the Server system.
Backspace and rewind tape operations have no meaning for VTL devices and do nothing.
mvBase Servers may be configured with as many VTLs as there are available virtual tape device LTUs. VTLs may be reconfigured as virtual tape files and vice versa.
Multiple LTUs may be configured as read devices corresponding to a single VTL write device, although only one of these read devices may be actively attached at a time.
When bidirectional tape transfer is desired, set up two separate VTLs using two pairs of LTUs with different pipenames and with each LTU write device on a different system.
See Also
Using the Tapes Tab to Add or Remove mvBase Tape Units
Remote Floppy Device Considerations