back-hdb does, and at least in 2.3.11 or later, is as robust as back-bdb.
I personally would avoid using back-ldbm if at all possible for numerous reasons. ;) And hopefully it'll be removed when 2.4 comes out.
I would make a care for ldbm as it doesn't seem to create as much i/o load as back-bdb. This is helpful with a large database.
--Quanah
-- Quanah Gibson-Mount Principal Software Developer ITSS/Shared Services Stanford University GnuPG Public Key: http://www.stanford.edu/~quanah/pgp.html