Universal Snapshot File Concept

Abstract

Snapshots are often used to perform on-line data backup, when storage is working without downtime. Nowadays, snapshots functionality is offered by several filesystems such ZFS, BTRFS or it can be achieved independently from the filesystem utilized, using block-device layer i.e. LVM. Existing snapshot is related to selected block device or filesystem technology, so it is not portable, especially when considered data are migrated to other filesystem. Concept of universal file snapshot is not limited by concrete filesystem, but it can be used in various file system. Universal snapshot file is based on the assumption that snapshot data are stored in special file. A version file that is related with considered universal snapshot file uses compensation process to provide access to previous version of original file data. In order to prevent the original file from corruption, all data modifications are separated by transactions, that use a journal file. Many other functionalities such as original file data history (local versioning) or point in time recovery utilize the universal snapshot file. The presented solution requires no user interaction. When one of original files is modified, all the necessary activities can be executed automatically. Moreover, universal snapshot file technology is transparent to the software that performs operations on selected original file.