I found that OSX acts different -- It actually allocates the entire size of the database on disk, regardless of how much is used. That may be common to all the BSDs.Sounds like whatever filesystem is default on BSDish systems doesn't support sparse files. Anyway, you can use mdb_stat to see what's in the MDB environment.
Oh, one additional note about the BSDs... I didn't see that behavior until I enabled writemap. Disabling writemap reverted it to the same behavior as linux, but then of course the advantage of writemap is lost. :P
--Quanah -- Quanah Gibson-Mount Sr. Member of Technical Staff Zimbra, Inc A Division of VMware, Inc. -------------------- Zimbra :: the leader in open source messaging and collaboration