A method includes a primary storage unit receiving a first write request including a first key and a first value; persisting the first value in a first non-volatile memory in association with the first key; broadcasting the first write request and a first set of globally-durable keys to secondary storage units; receiving, from the secondary storage units, an acknowledgement of the first write request and a first set of locally-durable keys, each of the first sets of locally-durable keys including the first key; the primary storage unit receiving a second write request including a second key and a second value; persisting the second value in the first non-volatile memory in association with the second key; and broadcasting the second write request and a second set of globally-durable keys to the secondary storage units, the second set of locally-durable keys including the first key. A system is also disclosed.