We have been working on another mnesia backend plugin, based on leveled. This would use much less ram than the mnesia backend.
But beware: this is work in progress, at all levels (epoch, mnesia_leveled and leveled). We have been able to run the full test suite with it, though. A pull request exists (marked as WIP). Leveled is implemented entirely in Erlang, except for the (optional) lz4 compression. So if you have time and are willing to play with it, feedback would be much appreciated.