How to sync only pruned and garbage collected backups to cold storage?

[watzr]

Hello!
I have a PVE set up here that consists of ~7tb of nvme-storage containing all my VMs and Data of those VMs (NAS, Nextcloud data "drives") - lets call this "maintank".
Now i want to backup these 7tb to an 8tb ZFS of 8tb HDD and SSD as special device to make pruning, garbage collection and verifying not take ages - lets call this "mainbackup".
In line with 3-2-1-backup-rule i want to have two offsite-cold-backup drives that i swap weekly - swap1 and swap2.

Now what i want is to prune, garbage collect and verify on "mainbackup" and then sync to swap1/swap2 so i dont have to prune/garbage collect/verify there because on HDDs that would take like a week.


"maintank" ---backup---> "mainbackup" - prune/GC/verify here ---sync---> "swap1/swap2" - dont prune/GC/verify here


Is this feasible or what would be a better way to do this?
I dont want to connect my swap drives to a special device because these are my "house burned down" desaster recovery that i want to be able to access without hassle and minimal risk.

Thanks in advance for any input

 

[fabian]

you need to prune or set remove_vanished, else the swap datastores will only ever grow. but you also need to run GC there, else the chunks of pruned/removed-via-sync snapshots are never cleaned up. if you verify or not is up to you of course - if you have redundant ZFS underneath you should be protected against bit rot anyway, and GC will detect any (logically) missing chunks.