A Virtual Tape must be 'rewound' before using the same logical tape device for a different Virtual Tape.

Virtual Tapes behave in an identical manner to physical reels of tape on physical tape drives.

When using physical reels of tape, the tape would be rewound (using the T-REW command) before the tape were removed from the drive (dismounted) and another different tape mounted.

A Virtual Tape must be also be rewound (using the T-REW command) before 'mounting' (using SET-TAPEFILE) a different Virtual Tape on the same Logical Tape Unit (LTU) .

Failure to do this may cause any data written to the second (newly mounted) virtual tape to start far into the tape at the point where the previous (just dismounted) virtual tape was positioned. The tape before that position will appear to contain blanks.

Rewinding the previous virtual tape before dismounting it and mounting a new virtual tape causes the new virtual tape to be positioned at the beginning of the tape.

The example below illustrates the problem

T-SELECT 5

SET-TAPEFILE C:\SALES\WESTERN.VTF

T-ONLINE

ACCOUNT-SAVE WESTERN.SALES

(Note no T-REW at this point!)

SET-TAPEFILE C:\SALES\EASTERN.VTF

ACCOUNT-SAVE EASTERN.SALES

T-REW

T-DET

At this point WESTERN.VTF is just fine, but EASTERN.VTF has as many nulls at the 'front' as there were characters in WESTERN.VTF.