Re: convert old full + differentials into new full

On 16/04/2021 19:36, imschmeg wrote:
> Is there a way to convert an old full backup (at time t0) plus a set of
> progressing differential backups off of that full backup (at times
> t1...tn) into a new full backup (at time tn) by only working with the
> backups themselves (not the original sources) and without restoring
> anything?

yes, this is possible, see FAQ for details:
http://dar.linux.free.fr/doc/FAQ.html#full-from-diff


> 
> I'd like to do this as a background task ocassionally, so that
> newer differential backups, after this background task has
> completed, can use the newer full backup as reference. 

if you just want to base a "differential" backup on the previous
"differential" backup (which method is also known as incremental backup)
no need to rebuild the full backup, just give to -A option the previous
differential/incremental backup.

hint: have a look at dar_manager to ease restoration of a particular
file from a possibly huge set of full, differential and incremental backups

> This way I can
> avoid having to do a new full backup from the sources,

Doing that will probably be slower than doing a new full backup, as you
will have to uncompress, eventually uncipher the old full backup the old
differential backup and manipulate than just reading the data from
filesystem... then in both cases dar will compress and eventually cipher
the resulting full backup.... I let you test and report the result of
your experimentation here, if you like ;^)

> and I can even
> offload the task of building the new full backup from the old one + the
> differentials onto a machine that doesn't have access to the original
> sources.
> 
> Ideally, I'd also like the original differental backups to be converted
> into decremental backups from the new full backup so that the old full
> backup can be discarded without losing any information.

Yes, that possible, funny idea, but pretty feasible! :)

...and always test or compare your backups as good practice.

> 
> 
> 


Cheers,
Denis

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