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
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