The invention relates to methods of snapshot operation for a data storage system with a host communicating with a cache memory, a source Virtual Logical Unit Number (VLUN) and a target VLUN, including generating first metadata (e.g., bitmaps and log files pointers) to locate first snapshot data and to indicate when the first snapshot data is in the target VLUN and generating second metadata to locate second snapshot data and to indicate when the second snapshot data is in the target VLUN, wherein the first and second metadata locate the same data in the target VLUN. The invention relates to systems that implement the methods. It relates to destaging data to maintain data consistency including reading metadata for snapshots, searching the metadata to identify snapshots that require original data to be destaged, destaging the original data to target storage, and updating metadata to locate original data and indicate destage completion.