The backup solutions described so far are full copies of a filesystem as it exists at that time. This snapshot is useful when you recognize a problem immediately and need the most recent snapshot to recover. It fails if you don't realize the problem until a new snapshot is made and the previous good data has been overwritten by current bad data.
An archive of a filesystem provides a history of file changes. This is useful when you need to return to an older version of a damaged file.
rsync, tar, and cpio can be used to make daily snapshots of a filesystem. However, backing up a full filesystem every day is expensive. Creating a separate snapshot for each day of the week will require seven times as much space as the original filesystem.
Differential backups only save the data that's changed since the last full backup. The dump/restore utilities from Unix support this style of archived...
