Re: [rdiff-backup-users] delete initial mirror

[Daniel Miller]

On Oct 21, 2009, at 10:03 PM, plug bert wrote:

>    Hmm...so in that case, if i want to incrementally back up a 100gb  
> file daily for one week, and for simplicity's sake, assume the file  
> grows 1gb per day, my backup media will need to be at least 100gb +  
> 6gb?

Yes... plus a bit of space for rdiff-backup housekeeping data.

>   i was kinda hoping for a method wherein we would just need to back  
> up the 100gb file at the beginning of the week, then just store the  
> deltas for the rest of the week. If recovery is needed, just apply  
> the deltas in reverse chronological order -- preferrably not being  
> dependent on earlier deltas to restore the file to a past point in  
> time...-

And how is that different from what you have been told that rdiff- 
backup actually does?


> > > >    We're looking into ways of
> >
> > > > performing incremental backups for mbox-style mailboxes; is
> > > > this setup possible:
> > > >
> > > > Sunday: make an initial mirror
> > > > Monday - Saturday: schedule incremental backup,
> > > > *delete* initial mirror

Incremental backups are useless without the initial full backup on  
which the increment is based. I don't understand how you think you can  
delete the initial mirror here and still maintain the ability to  
recover files from your incremental backups.

In the case of rdiff-backup, you will always have a full image of what  
existed when the most recent backup occurred. In addition to that you  
can have an arbitrary amount history consisting of REVERSE increments  
(limited only by the amount of space on your backup volume). rdiff- 
backup can apply the reverse increments to recover files as they  
existed in the past.

> > > > Sunday: make initial mirror(i.e. reformat the
> > > > mirror drive, start from scratch)
> > > >
> > > > Monday - Saturday : incremental backup again


In the scheme you have described when you re-format the backup volume  
on Sunday you will obviously lose all of your history, so on Monday  
you only have 1 day of history. The rdiff-backup scheme is potentially  
much better since it can maintain 7 days of history at all times. To  
do this you will run rdiff-backup twice each day, once for the daily  
backup and once to remove increments that are older than 7 days.

~ Daniel