Retention Policy, what is done just before deletion is made?

Hello all,

I’m trying to understand how Kopia Retention policy is working in more details.
To make my question below more clear, I will imagine the following example:

Retention Policy:
“daily retention”: “7”, all other policies are set to “0”.

09.09.2024 - backup-daily-1 (22GB)
10.09.2024 - backup-daily-2 (+1GB)
11… - …
12… - …
13… - …
14… - …
15.09.2024 - backup-daily-7 (+1GB)
16.08.2024 - ???

To make this example more precise, I wrote some numbers behind in brackets. These shall represent the size of each backup. Each day new data of 1GB comes on top.

Question(s): What will happen with “backup-daily-1” on the 16.09.2024? What will happen with the content of “backup-daily-1”, since the data still is in the source folder (which shall be backup’ed).
In case “backup-daily-1” is going to be deleted, will there be a check upfront, if the data is the same as it is on the source folder? Means, not the whole package need to be uploaded again?

thanks in advance!
Rob

Snapshot will be deleted but only unreferenced data will be deleted. If any data is in use by other snapshots it is kept.

If not sure use --dry-run to experiment.