Featured is a data storage back-up system for replication, mirroring and/or backing-up data including one or more first and second data storage devices that embody iSCSI, FC or alike principals and that are operably coupled to each other preferably via a WAN. The first data storage device is configured and arranged so there are two writes of data, one write to a persistent storage device from which reads are done and another write to a SAPS device wherein the data is saved using log-structured file system (LSF) techniques. After saving data to the First storage device, the data logs in the SAPS device are communicated to the second data storage device whereat a de-staging process is conducted so as to de-stage the data logs and write the de-staged data to a persistent storage device in the second data storage device.