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 can be a very nice optimization for your backups. Basically, imagine that you have 100 nearly identical Windows or Linux machines 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 saved and restored.

The Job directive Base=Jobx, Joby… permits you to specify the list of jobs that will be used during a Full backup as base.

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

Job {
    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 FileSet chapter.

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

Important note : The current implementation doesn’t permit to scan a Volume with the bscan facility. The result does not permit the restore of files. It is therefore recommended to not prune File or Job records with Basejobs in use.

The “M” option letter for the Accurate directive in the FileSet Options block is the recommended option for Jobs that refer to BaseJobs as it will backup files based on the last backup time, which is more useful, because the mtime/ctime timestamps (“m” and “c” accurate option letters, respectively) may differ on various Clients, causing unnecessary files to be backed up.

Job {
    Name = USR
    Level = Base
    FileSet = BaseFS
    ...
}

Job {
    Name = Full
    FileSet = FullFS
    Base = USR
    ...
}

FileSet {
    Name = BaseFS
    Include {
        Options {
            Signature = MD5
        }
        File = /usr
    }
}

FileSet {
    Name = FullFS
    Include {
        Options {
            Accurate = Ms # check for mtime/ctime and Size
            Signature = MD5
        }
        File = /home
        File = /usr
    }
}

Base Jobs are not compatible with Copy or Migration Jobs.