Storage snapshots are divided into Copy-on-Write (CoW) and Redirect-on-Write(RoW). The two methods for snapshots differ in performance and in how and on which hard disk they create the history directories.
Copy-on-Write, which stands for" copy while writing", copies are made when a user has modified copies. This reduces the number of copies. With the CoW method, the metadata of the snapshot is also saved with the first snapshot. Afterwards, only changes to data blocks compared to the previous snapshot are saved. No records are overwritten and each initiated operation is either fully executed or ignored. Aborted operations can be restored to the starting point. The snapshot and history data are stored sequentially on separate hard disks.