We converted from LEGATO to ADSM about 18 months ago.  There were a
number of reasons we cut over some of them are:        Better performance ---
 our backup time was reduced by about half
ADSM took full advantage of 3490 technology LEGATO would only use half of the
cartridge.
At the time ADSM could retain files that have been deleted off the system for
60 days -- (in our case) .  LEGATO wouldn't do this
Restoring a file system is about 80% faster with ADSM over LEGATO

    John O'Connell
    Siemens ROLM Communications