Do you need to back up (not snapshot, but full copy of data) DB if you have Multi-AZ standby DB instances?

Question

I understand that database backup is a full copy of the database and serves as the last resort in a disaster where data is lost -- recovering data.

In the case of multi-AZ standby db deployment, we already have multiple copies of the data, thus it's unlikely that all of them will be destroyed. With that in mind, do we still need database backup in this case? Or we can just use the other standby instances as backup?

Note that I'm not talking about snapshot here. I do understand we still need to take snapshots to revert changes in case of an accidental change or human error.

Answer 1

Multi-AZ is backup only within same region . It does not protect you from data loss caused by entire region outage or destruction.

For mission critical databases you can either create read replica in a different region for live backups, or a cheaper solution is to copy db snapshots to different region on periodic basis.

Answer 2

What I do not undersdtand here is the emphasis on the word backup . RDS snapshot is a whole backup of the instance. You can recover the whole rds instance with all the settings from the snapshot. So it's a backup . It's better to have a backup retention policy from 1(0 being no backup) upto 35 days(which by the way are snapshots).
As Marcin already talked about, it's better to have a read replica which can help with performance as well as can act like a backup. Anything happens to the main db, you can promote read replica to the main.