XOA "Key Backups" & Key Backup behaviour.

Hello, I am sorry if this is a question that was asked before. I searched around a bit and couldn’t find any similar questions, nor could I find any documentation that answered my questions.

I am running XCP-ng with Xen Orchestra for my homelab, however when trying to debug some behaviour and get a better understanding of how everything works I noticed a couple different interesting behaviours:

Key backups, key backups as far as I understand mean that it is kept for longer term storage, so if my understanding is correct, assuming I make 1 backup every 4 hours of the day, retain 12 backups in the schedule, and retain 3 days of backups, 4 weeks of backups and 6 months of backups this should happen:
[(Key) Full Backup 1]→[Delta 1]→[Delta 2]→[Delta 3]→…→[Delta 14] For daily.
When the day ends:
[(Key) Full Backup 1]→[(Key) Daily Backup 1]→[Delta 1]→…→[Delta 14] For daily.
And then once that day ends we have this:
[(Key) Full Backup 1]→[(Key) Daily Backup 1]→[(Key) Daily Backup 2]→[Delta 1]→…→[Delta 14] For daily.

So if my understanding is correct a key backup is purely a backup that would be stored long(er) term?
And so when the week would end and a new weeks starts, all daily backups of last week would be squashed and merged into a new key backup that contains everything for the week?

A key backup is essentially the first, full backup in an incremental backup chain. When you set up a job to perform incremental backups of a virtual machine (VM), the system must first create a complete, full backup of the VM’s disks. This initial backup is what’s referred to as the “key backup.” It acts as the foundation or reference point for all subsequent incremental backups.

Hey Tom.

Thank you for the response, I however encountered seemingly different behavior;
When I add schedules to backup say once a day, I will have a key every single day by the looks of it, however based on the size it cannot possibly be a full backup.

Thank you for your response!

I have a delta backup job with a retention of 4 and a full backup interval of 20 which shows like this.

https://docs.xen-orchestra.com/incremental_backups#key-backup-interval