DMAPI

erm .. i think you mean XDSM which is a specification for Data Management (DM) applications which also specified an API (XDSF is the security framework) .. but, you're right - DMAPI was really the interface to the specification that defines multiple APIs to deal with DM .. IBM and SGI really latched onto this since it meant that they didn't have to rewrite their global filesystems (GPFS, [C]XFS) to deal with EAs, offline/partials/etc, region mgmt and auth, etc ..

the big problem with DMAPI is that it simply doesn't scale .. take a look at the NERSC/LBNL paper for some hints at some of the architectural issues .. metadata scan performance is ultimately key, and the ability to abstract this away when necessary can be quite valuable