I've been looking at this problem as well.

>Can you use a special management class for the Informix logs?

Since Onbar never tells ADSM that the files have been deleted, they never
go into ADSM's expiration routine.  As far as ADSM knows, these are still
live files on the system.  As such, they will never be deleted out of
ADSM regardless of management class settings, since ADSM will always keep
one active version of a file it thinks still exists.

A meat-cleaver way of doing it is to turn off reclamation and once a tape
contains only expired logs, delete the tape with discard data=y.  That's
really ugly -- ther has to be a better way.