Déjà Dup

Deja Dup - Full Backups - When and how, exactly?

Asked by JaSauders

How does Deja Dup determine when new full backups are needed? Yesterday when I tried to run a manual backup it failed on two or three occasions. Afterwards I ran a manual backup again and it said to prevent corruption it would do a full backup that would take a bit longer than normal. Is Deja Dup able to sense a corrupt backup? Is that what happened in my case?

Also, if I select to keep backups for a week, what is the process that Deja Dup follows? Is it full backup on day 1, incremental on 2 3 4 5 6 7, and then another full backup on day 8? Is that how it works?

Thank you guys for an excellent backup utility. I'm just trying to understand Deja Dup's technical side a bit more. Thanks!

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Michael Terry (mterry) said : 		#1

See https://live.gnome.org/DejaDup/HowItWorks#Full_Backups for a rationale of why we do the occasional full backup.

The exact decision making process is a little complicated. It's a formula based on how often you automatically back up and how long you've asked Deja Dup to keep backups. The bottom line is anywhere from 1 month to 6 months. The less aggressively you back up, the longer it will wait.

One of the ideas is to try to keep at least two full backups around at all times.

You can see the gory details here: http://bazaar.launchpad.net/~deja-dup-hackers/deja-dup/20/view/head:/common/CommonUtils.vala#L513

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JaSauders (jasauders) said : 		#2

So essentially Deja Dup does a number crunch based on how often I back up and on the fly does full backups when it deems necessary entirely out of precaution? That's kind of interesting. I just wonder how often I'd see "creating full backup" if I were to do weekly backups instead of daily.

I would also assume that Deja Dup is intelligent enough to differentiate backup 1 vs backup 2? Because if the user goes to Deja Dup and hits restore, I would think Deja Dup would be smart enough to give them last week's full backup instead of last month's full backup. Would I be correct here?

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Michael Terry (mterry) said : 		#3

In your example, assuming you have "Keep backups" set to "Forever", backing up daily will cause a new fresh backup every month. Backing up weekly will cause one every three months.

Yes, if you restore, Deja Dup defaults to the most recent backup data (which may be an incremental one). It only uses data from older full backup chains if you specify an older date.

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