Because a Fast Backup will not scan the destination (except on the first run after it is enabled for that profile) that means only the changes will be applied to the destination without regard to what is actually on the destination. It is an incremental (or differential) backup. For example, you could change the destination directory, run the profile, and then only the new/modified files would be copied to the destination (and not all the files as would normally be the case).

This has important consequences when your destination directory is dynamic, i.e. it uses environment variables that can change in value. For example:

  • Create a normal backup profile and set the source directory to C:\My Documents and the destination directory to D:\Backup\%DAYOFWEEK%
  • Enable Fast Backup for the profile.
  • On the first run of the profile (let's assume it's Monday and the destination directory is empty) all the files will be copied to D:\Backup\1
  • When the profile is run on Tuesday then only the new or modified files will be copied to D:\Backup\2
  • On Wednesday new and changed files will be copied to D:\Backup\3 and so on until Monday.
  • When it is run again on the following Monday then only the new and changed files will be copied to D:\Backup\1

This creates a complete mess as it's difficult to know which is the latest version of a file and where it is stored. It is very difficult to restore from. The solution to this is to change the backup configuration so that (in the above example) a full backup is done on Monday, and fast backups are done on all other days.

There are three ways to do this (using this example):

  • The best and easiest option is to configure the Force a re-scan when: settings to force a re-scan every Monday (select %DAYOFWEEK% from the list, select equals from the drop-down, and type in 1 (1=Monday, 7=Sunday) in the edit box).
  • You can do this manually by clicking the Force Re-scan button on the Mondays.
  • Use the -full command line parameter (for Monday only when scheduling). See the help file for a complete list of command line parameters.