There are two concepts about backup subject. A file-level backup is oriented to store separate files. A volume-level backup or imaging is oriented to store whole filesystem of a volume.

A file-level backup naturally provides an intuitive and flexible way to select objects to store. File-oriented backup tools allow to choose any combination of both local and network accessible files. A file-level data restoration allows to selectively restore only damaged files without affecting other ones. However, there are important file-related system objects which are not files and usually cannot be stored, restored and even accessed from a file level.

A volume imaging can store files and any associated metadata including distribution information, security data, quotas, extended attributes, named streams, multiple hard and symbolic links and so on. Imaging tools generally provide higher backup performance because they do not involve filesystem drivers to the process. In addition, they can backup offline filesystems including ones not being supported by a host operating system. A data restoration generally does not require a host operating system to run, so that imaging technique is a perfect choice for system cloning and disaster recovery tools. Disadvantages of volume imaging are that it cannot be applied to remote resources and a general ineffectiveness of backup and restore of selective files within the volume-imaging framework.

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