Item 1:   Specify a minumum number of backups to retain
  Origin: Mark Bergman <mark.bergman AT uphs.upenn DOT edu>
  Date:   Mon, 30 Nov 2009
  Status:

  What: Add an option ("Keep Mimimum") to specify that a minimum number of
        backups (per-level and per-client) should be retained, over-riding
        the other retention policies. If the number of existing backups
        is less than or equal to the specified minimum, then the existing
        backups are not purged.

        Example:

                JobDefs {
                        Name = "DefaultJob"
                        Type = Backup
                        FileSet = "Default"
                        Pool = Incremental
                        Full Backup Pool = Full
                        Incremental Backup Pool = Incremental
                        Keep Mimimum Full = 1
                        Keep Minimum Differential = 1
                        Keep Minimum Incremental = 0
                }


        Those settings ("Keep Mimimum") could be specified in the per-client
        job definition, which would take precedence over the default...but that
        is unlikely usage.

  Why:  Particularly as data volumes increase, the frequency of full backups
        decreases. This leads to a situation where there may be very few full
        backups, run at long intervals. A failed backup or other schedule
        change can result in such a long interval between jobs that the
        remaining full backups are expired and purged before a new backup has
        completed successfully. Without a full backup as a reference point, a
        complete restoration is impossible.

        This option would also alleviate the problem of incremental backups
        being unexpectedly promoted to "full" because the last full backup
        was purged. That promotion can be difficult to deal with if it 
        occurs outside of a schedule (ie., there may not be enough media
        or storage space available for the backup, running full backups may
        be so disruptive that they are scheduled for specific maintenance
        windows, etc.).

  Notes: If the mimimum number of backups to retain defaults to "0" then the
        current behavior is unchanged. A setting of "1" (the recommended option
        for full backups) would instruct bacula not to purge the last
        remaining full backup for a client until the next backup at that level
        succeeds.

        This option requires no changes to the basic retention algorithm...it's
        a test that would be applied after all existing retention/recycling/
        purging decisions have been made, but before the action takes place.

----
Mark Bergman                              voice: 215-662-7310
mark.bergman AT uphs.upenn DOT edu                 fax: 215-614-0266
System Administrator     Section of Biomedical Image Analysis
Department of Radiology            University of Pennsylvania
      PGP Key: https://www.rad.upenn.edu/sbia/bergman 



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