How does VDP incremental backup really work?

Hi,

I'm a little bit confused about how VDP incremental backup really work.

Let's say I use 7 days retention policy.

On the first day, VDP does full backup. Then on, the subsequent backups after full backup are always be incremental.

My questions are:

1. On day 8, VDP would run another backup job. To comply with the policy, will VDP delete backup on Day 1 or will it merge Day 1 & Day 2 backups into one? My confusion is, if VDP delete backup on Day 1, the subsequent backups after full backup will be useless.
2. If VDP does merge Day 1 & 2 backups, what type of backup (full or incremental) would VDP do on Day 8?

I hope my questions are clear enough.

Note: I'm using VDP 5.1 (if there is any behavior difference between 5.1 & 5.5).

Thank you.

Regards,

Apenk