Amazon RDS manual snapshot conjunction with automated backup?

Question

I've read through the Amazon doc, and searched through countless of posts in SO but still I've not been able to answer 2 questions.

Situation: As I understand, Amazon RDS snapshots are incremental. But how can manual snapshots play nice with automated snapshots feature ? Imagine I have created a script to snapshot the DB every day at 1 A.M. and copy the snapshot to another region. Then the snapshots will be:

+ Day 1 - 1 A.M.: snapshot 1 (manual) => copy to the other region (first time, full copy)
+ Day 1 - 6 A.M: snapshot 2 (automatic backup), in current region, not copy.
+ Day 2 - 1 A.M.: snapshot 3 (manual) => copy to the other region (incremental)
+ Day 2 - 6 A.M: snapshot 4 (automatic backup), in current region, not copy (incremental)

Question 1:

snapshot 3 = changes since snapshot 1 or snapshot 3 = changes since snapshot 2 ?

Question 2:

If I just copy snapshot 1 and snapshot 3 (manual snapshots) to another region, is it enough to restore the database ?

In storage world, snapshot 3 = changes since snapshot 2, and we must have all the incremental snapshots (1+2+3+4) to reconstruct the original volume. But for AWS, there're implications and I'm not so sure.

Thank you.

Answer 1

Question 1: snapshot 3 = changes since snapshot 2

Question 2: If you copy a snapshot to another region, the first copy will become a full snapshot and not an incremental and yes you would be able to restore the database from a copied snapshot. Subsequent snapshot copies will be incremental based upon the last copied snapshot.

Once a DB Snapshot is copied to a specific AWS Region, any subsequent copy operations of the DB Snapshots of the same DB Instance to that Region will only transfer the data that has changed since the last copy. Thus the subsequent copy operations transfer fewer amounts of data and complete faster.

copy of Amazon RDS DB Snapshots across AWS Regions