rsync - Sep 2007 - Verifying understanding of backup-dir vs compare-dest

Hello,

  Say one starts with creating an archive 

       rsync work -> archive

  and periodically (below, i = 1 to N) does 
      
       rsync --backup-dir=a_<i>      work -> archive
  and  rsync --compare-dest=archive  work -> b_<i>

  Then suppose one wants to recover the work directory as it was at
  time k.

  Using the b_<i> directories, one would merely merge b_k with the
  archive directory.

  But using the a_<i> directories one would have to merge a_<j> with
  archive starting with j=N and going down sequentially to j=k.

  Is my understanding correct?  More importantly, I would like to
  know under what conditions and for what goals people use
  --backup-dir;  and likewise when and why do people use
  --compare-dest?
  
  Thanks,
  
  --Suresh

On 9/12/07, Suresh Govindachar <sgovindachar@yahoo.com>
wrote:
>   Say one starts with creating an archive
>
>        rsync work -> archive
>
>   and periodically (below, i = 1 to N) does
>
>        rsync --backup-dir=a_<i>      work -> archive
>   and  rsync --compare-dest=archive  work -> b_<i>
>
>   Then suppose one wants to recover the work directory as it was at
>   time k.
>
>   Using the b_<i> directories, one would merely merge b_k with the
>   archive directory.
>
>   But using the a_<i> directories one would have to merge a_<j>
with
>   archive starting with j=N and going down sequentially to j=k.
>
>   Is my understanding correct?
Yes, those procedures for recovery are correct.

Matt