The VSTORE command of MPE/iX has a role in system backup verification. It's good standard practice to include VSTORE in every backup job's command process. Using VSTORE is documented in the manuals for the original OS in which it was introduced: 5.0.
If possible, do your VSTOREs on a different (but compatible model) of tape drive than the one the tape was created on. Why? DDS tape drives slowly go out of alignment as they wear.
In other words, it's possible to write a backup tape, and have it successfully VSTORE on the same drive. But if you have to take that same tape to a different server with a new and in-alignment drive, you could have it not be readable!
If you'll only ever need to read tapes on the same drive as you wrote them, you're still not safe. What happens if you write a tape on a worn drive, have the drive fail at some later date -- and that replacement drive cannot read old backup tapes?
Using the 'two-drive' method to validate backup (and even SLT) tapes is a very prudent choice, if you have access to that array of hardware. It can also often help identify a drive that's going out of alignment -- before it's too late!
Unfortunately, SLTs have to be written to tape (at least, for non-emulated HP 3000s). However, your drive will last years longer if you only write to it a few times a year.