A data storage system can have one or more hosts connected to a data storage subsystem with the host having a host processor and the data storage subsystem having a controller. Write back data generated at the host triggers the host processor to allocate a cache location in the data storage subsystem where the generated data is subsequently stored. The generated write back data is written in a non-volatile destination address as directed by the controller prior to waiting for a secondary event with the generated data stored in both the cache location and the non-volatile destination address. Detection of the secondary event prompts the controller to signal the host processor that the cache location is free for new data.