[rdiff-backup-users] Feature request: support for backup levels

[Olaf Dabrunz]

Hello,

I most dearly miss support for backup levels. They would add the
advantages of better control over the
    - backup size
    - restore speed
    - coverage and granularity of backups
(as you may know...).

ATM, my backup volume is filling up more and more with every increment
that is created. With increments, that size of the backup is

    backup_size ~ size-of-data + ( #-of-incremental-backups *
                                average-size-of-an-incremental-backup )

and so it grows with each of my daily backups.

ATM, for me this means:

          74 GB = 69 GB + ( 80 (daily backup for ~ 3 months) * 62.5 MB )

When I need or want to save space, currently the only option that
rdiff-backup gives me is to delete old increments (so I cannot get old
files back anymore).


Backup levels would give me the ability to
    - create "increments" that are based on the state from an older
      "increment" ("increments" may now be called differentials)
    - overwrite unneeded old "increments" with newer "increments".

This would allow for keeping the number of increments constant and
for minimizing the duplicate information in the increments, while
keeping some redundancy.
    
The backup size becomes

    backup_size ~ ( #-of-level0-backups * size-of-data ) +
                    ( #-of-"incremental"-(level[1-x])-backups *
                      average-size-of-an-"incremental"-(level[1-x])-backup )


The backup scheme I want to use may look like this:



level8                  *                    *                    *       
level7                     *                    *                    *
level6            *                    *                    *         
level5               *                    *                    *      
level4      *                    *                    *               
level3         *                    *                    *            
level2                        *                                       
level1                                             *                  
level0   *                                                            
        01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21
        Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa


This means I keep one full (level0) backup and only 8 "increments"
(differentials). A restore would have to look at up to 5 "increments" to
collect all data (all diffs). I can restore all files up to one week
backwards. By using more levels/"increments", I can extend that period
or introduce snapshot "increments" (e.g. at the last four Sundays, then
at the beginning of the last four months, etc.).

The real advantage is that the backup size only grows with the size of
the data and the size of the changes of the data, not the number of
invocations of the backup program. Also, by buying more backup space I
can increase the coverage of the backup (longer time backwards, by using
snapshots and/or more "increments") and/or its granularity (more levels
for the "incremental" scheme).

Regards,

-- 
Olaf Dabrunz (od/odabrunz), SUSE Linux Products GmbH, Nürnberg