You won't have problems comparing Bus-Tech's new mainframe rig to other systems because, well, I don't know of anything similar in that space. However, the MDL-4000 (Mainframe Data Library) is the logical equivalent of a VTL (virtual tape library) with the significant distinction of having no data stored inside the unit.

Like a conventional VTL, the MDL-4000 attaches to an IBM or Unisys mainframe via FICON or ESCON and can emulate as many as 1,024 tape drives (model IBM 3480 or 3490). You can direct your applications to write to these ghost tape drives without major changes.

The MDL-4000 will direct all the tape data to its own connected NAS devices. The unit supports a variety of NAS solutions from many vendors, according to Bus-Tech, or you can attach an EMC Centera or a NetApp SnapLock if compliance is a concern.

At a starting price of about $110,000 without any NAS devices -- that's small change in the mainframe world -- the MDL-4000 will probably make you feel that storage is not so expensive after all.

Join me on The Storage Network (http://weblog.infoworld.com/thestoragenetwork) with questions or comments.