Embodiments of the invention relate to a para-virtual I/O system. A consistent para-virtual I.O system architecture is provided with a new virtual disk interface and a semantic journaling mechanism. The virtual disk interface is extended with two primitives for flushing and ordering I/O, both of the primitives being exported to para-virtual I/O drivers in a guest operating system. The ordering primitive guarantees ordering of preceeding writes, and the flushing primitive enforces order and durability. The guest drivers selectively uses both of these primitives based on semantics of the data being persisted from the para-virtual cache hierarchy to physical disk. The order of committed writes is enforced in order to enable a consistent start recovered after a crash.