An overlay snap is generated by generating a snapshot of a logical storage volume, writing a data stream to the overlay snap, generating pointers indicating locations of new data written to the overlay snap, and generating null pointers for locations that do not have new data written to the overlay snap. The overlay snap comprises the pointers and the null pointers. The overlay snap may be applied to a volume to generate a current snapshot of the volume. The overlay snap may be used maintain write order fidelity during continuous data replication by creating a copy of a snapshot on a target storage device and writing new data to an overlay snap on the target storage device.