# File Deduplication using Base Jobs

A base job is sort of like a Full save except that you will want the FileSet to contain only files that are unlikely to change in the future (i.e. a snapshot of most of your system after installing it). After the base job has been run, when you are doing a Full save, you specify one or more Base jobs to be used. All files that have been backed up in the Base job/jobs but not modified will then be excluded from the backup. During a restore, the Base jobs will be automatically pulled in where necessary.

This is something none of the competition does, as far as we know (except perhaps BackupPC, which is a Perl program that saves to disk only). It is big win for the user, it makes Bacula stand out as offering a unique optimization that immediately saves time and money. Basically, imagine that you have 100 nearly identical Windows or Linux machine containing the OS and user files. Now for the OS part, a Base job will be backed up once, and rather than making 100 copies of the OS, there will be only one. If one or more of the systems have some files updated, no problem, they will be automatically restored.

A new Job directive `Base=Jobx, Joby...` permits to specify the list of files that will be used during Full backup as base.

    Job {
       Name = BackupLinux
       Level= Base
       ...
    }

    Job {
       Name = BackupZog4
       Base = BackupZog4, BackupLinux
       Accurate = yes
       ...
    }

In this example, the job `BackupZog4` will use the most recent version of all files contained in `BackupZog4` and `BackupLinux` jobs. Base jobs should have run with `level=Base` to be used.

By default, Bacula will compare permissions bits, user and group fields, modification time, size and the checksum of the file to choose between the current backup and the BaseJob file list. You can change this behavior with the `BaseJob` FileSet option. This option works like the `verify=` one, that is described in the FileSetFileSetResource chapter.

    FileSet {
      Name = Full
      Include = {
        Options {
           BaseJob  = pmugcs5
           Accurate = mcs
           Verify   = pin5
        }
        File = /
      }
    }

Important note: The current implementation doesn't permit to scan volume with bscan. The result wouldn't permit to restore files easily.