Re: Going deeper on merge feature

On Sunday, December 17th, 2023 at 02:49, Denis Corbin - dar.linux at free.fr <dar_linux_at_free_fr_bkyxcbq-Xswo3RjJnUcnd4MvtDKV2g@public.gmane.org> wrote:

Hello Denis, 
thank you for replying so fast and accurately. 
Sorry for my late reply, I took some time to study the docs comparing it with what you had explained. 

> first I understand that 2021_diff-backup is a differential backup
> (according the name and the fact it contains 'deleted'
> files, as you mentioned).
> 
> My question is: what was the backup of reference for 2021_diff? Was it
> 2020_full-backup or another backup?
> 
> Let's assuming the reference backup was 2020_full-backup and consider
> this command-line:
> 
> dar -+ merged -A 2020_full -@ 2021_diff -/Oo
>

You understood correctly. 2020_full was the backup reference of 2021_diff. Sorry for not being clear enough by my side.
 
[...]
> what you are not taking into account here, is:
> 1/ that an entry that has not changed since the backup of reference is
> stored as en empty shell in the diff backup: there is only the metadata.
> This get the flag "unsaved".
> 
> 2/ When a file has been removed between the full and the diff backup,
> the diff contains a special entry telling that the file has been
> removed. (to be able to remove the file from filesystem when restoring
> the differential backup).
> 
> For those two previous case, the overwriting policy keep in the
> resulting archive the "Unsaved" version of files and the "deleted"
> entries. Both cannot be used to restore anything from them.
> 

Thank you to have explained it clearly. Actually, that was the status I observed during my tests.
I still wonder why "-/ Oo" doesn't seem to be the default overwrite policy as it is reported by the documentation.

[...]
> Now, if you plan is to make a full backup from the diff backup as if a
> full backup was done at the time of the diff backup, this is as easy as
> adding "full-from-diff" in your merge pattern.

That's exactly what I meant and want to do.

> 
> I let you first examin the /etc/darrc provided with dar, where the
> "full-from-diff" definition contains the adhoc overwriting policy and a
> quick documentation on how to use it.
> 

Thanks a lot for this precious hint. I applied that policy and actually reached my goal.
Docs mentions that logical operators must be escaped if they will be typed in a CLI. I realized that only after having done the merge, then I didn't used any of them. Anyway, It seems to be I reached my goal. I'll be more careful next time. 
I didn't know how to treat the "Saved status" but now, I understood that's possible through the "conditions mechanism". That's not really easy to understand to me, but I feel I understood the most of it. I'll do some more test on it just for learning purpose.

> Cheers,
> Denis

Thanks a lot.
--
vash