If you use the default mode MDB_SYNC then it's reliable but can be slow for writes. For max write performance you need MDB_NOSYNC (IIRC that's what the official benchmarks use) but then the whole database can be unrecoverable in case of crash. It has happened to me.
Sqlite in WAL mode will never lose all your data and performance can be configured vs durability by setting pragma synchronous to full or normal.
Comments
If you use the default mode MDB_SYNC then it's reliable but can be slow for writes. For max write performance you need MDB_NOSYNC (IIRC that's what the official benchmarks use) but then the whole database can be unrecoverable in case of crash. It has happened to me.
Sqlite in WAL mode will never lose all your data and performance can be configured vs durability by setting pragma synchronous to full or normal.