A system includes a first storage unit connected to a secondary storage unit such that data written to the first storage unit is replicated on the secondary storage unit. The first storage unit in at least one embodiment includes the capability to intercept input/output instructions for routing to a buffer and/or directly to the secondary storage unit. A method for operation of a first storage unit includes intercepting a data operation from a requesting client, determining whether the data operation modifies data. When no modification of data is required, the method retrieves the requested data from the first storage unit and transmits the requested data to the requesting client. When a modification of data is required, the method performs the data operation in the first storage unit, stores the data operation in a buffer, transmits the data operation from the buffer to the second storage unit, receives a confirmation from the second storage unit is done, and deletes the data operation in the buffer.