[Duplicity-talk] Concept and how to combine incremental and full backups to save space

[c . buhtz]

Hello together,

I am sorry for asking because I assume the answers are still out there. 
But I wasn't able to find the needed information's or I wasn't able to 
understand them and bring them together in my head.

In the duplicity docs it is recommended to not make the chain of 
incremental backup's to long. Make it one month and then do a full 
backup. OK, I understand why.
Technically I do not know how to "implement" this. Can I combine 
switches/options that way that I only need one duplicity call and 
duplicity decide itself if it has to do a incremental or full backup?

Currently I call duplicity with this (folders replaced by placeholders):

duplicity SOURCE_FOLDER file:///DESTINATION_FOLDER --no-encryption 
--progress --verbosity INFO --volsize 500

I have very limited space on the destination. I think I am not able to 
hold two full backups there. I only can have one full backup at time.

This is my current collection status where I have one (old) full and lot 
of incremental.

Last full backup date: Fri Dec  3 09:44:22 2021
Collection Status
-----------------
Connecting with backend: BackendWrapper
Archive dir: 
/home/user/.cache/duplicity/50d0997d52a684176de033baca98f9f0

Found 0 secondary backup chains.

Found primary backup chain with matching signature chain:
-------------------------
Chain start time: Fri Dec  3 09:44:22 2021
Chain end time: Thu Mar 17 09:23:28 2022
Number of contained backup sets: 26
Total number of contained volumes: 50
 Type of backup set:                            Time:      Num volumes:
                Full         Fri Dec  3 09:44:22 2021                25
         Incremental         Fri Dec  3 10:25:03 2021                 1
         [snipped 20 incrementals]
         Incremental         Tue Mar  8 08:45:37 2022                 1
         Incremental         Thu Mar 10 11:25:11 2022                 1
         Incremental         Wed Mar 16 17:41:44 2022                 1
         Incremental         Thu Mar 17 09:23:28 2022                 1
-------------------------
No orphaned or incomplete backup sets found.

There is definitely not enough space to create a second full backup. 
Maybe I can transform the incremental's into a second full so that there 
are no incremental's anymore consuming space. When I have two fulls I 
can delete the older one and go on with new incremental's (for one 
month). Is this a good plan? :)

Kind
Christian