Explanation
to Increase disk performance by using NVMe disks you can use Dense IO Shape also as the number of CPUs will not change so we should VM.DenseIO2.16

Explanation
Database backups can fail for various reasons. Typically, a backup fails because either the database host cannot access the object store, or there are problems on the host or with the database configuration.
First need to determining the Problem
In the Console, a failed database backup either displays a status of Failed or hangs in the Backup in Progress or Creating state. If the error message does not contain enough information to point you to a solution, you can use the database CLI and log files to gather more data. Then, refer to the applicable section in this topic for a solution.
Database Service Agent Issues
Your Oracle Cloud Infrastructure Database makes use of an agent framework to allow you to manage your database through the cloud platform. Occasionally you might need to restart the dcsagent program if it has the status of stop/waiting to resolve a backup failure.
Object Store Connectivity Issues
Backing up your database to Oracle Cloud Infrastructure Object Storage requires that the host can connect to the applicable Swift endpoint. You can test this connectivity by using a Swift user.
Host Issues
One or more of the following conditions on the database host can cause backups to fail:
- Interactive Commands in the Oracle Profile
- The File System Is Full
- Incorrect Version of the Oracle Database Cloud Backup Module
- Changes to the Site Profile File (glogin.sql)
Database Issues
An improper database state or configuration can lead to failed backups.
- Database Not Running During Backup
- Archiving Mode Set to NOARCHIVELOG (When you provision a new database, the archiving mode is set to ARCHIVELOG by default. This is the required archiving mode for backup operations)
- Stuck Database Archiver Process and Backup Failures
- Temporary Tablespace Errors
- RMAN Configuration and Backup Failures
- RMAN Retention Policy and Backup Failures
- Loss of Objectstore Wallet File and Backup Failures
TDE Wallet and Backup Failures
- Incorrect TDE Wallet Location Specification
- Incorrect State of the TDE Wallet
- Incorrect Configuration Related to the TDE Wallet
- Missing TDE Wallet File
As this is not new provisioned database and already in the ARCHIVELOG , regular backups of DB system to OCI object storage in places, so the best answers are,
- Ensure that your database host can connect to the OCI object storage
- Restart the database service agent

Remote VCN peering is the process of connecting two VCNs in different regions The peering allows the VCNs' resources to communicate using private IP addresses without routing the traffic over the internet or through your on-premises network.

health check A test to confirm the availability of backend servers. A health check can be a request or a connection attempt. Based on a time interval you specify, the load balancer applies the health check policy to continuously monitor backend servers. If a server fails the health check, the load balancer takes the server temporarily out of rotation. If the server subsequently passes the health check, the load balancer returns it to the rotation.
You configure your health check policy when you create a backend set. You can configure TCP-level or HTTP-level health checks for your backend servers.
- TCP-level health checks attempt to make a TCP connection with the backend servers and validate the response based on the connection status.
- HTTP-level health checks send requests to the backend servers at a specific URI and validate the response based on the status code or entity data (body) returned.
The service provides application-specific health check capabilities to help you increase availability and reduce your application maintenance window.

Explanation/Reference:
Reference https://docs.cloud.oracle.com/en-us/iaas/Content/Block/Tasks/restoringavolumefromabackup.htm