Changing Storage GP2 to GP3 in AWS RDS

Changing storage from GP2 to GP3 for your MySQL 8.0.42 RDS instance in production will not cause any downtime. When you initiate this storage type change, your instance will enter a "storage-optimization" status, but it will remain fully operational during this process.

The storage optimization process duration varies depending on several factors. It's usually short but can sometimes take up to 24 hours or more. During this time, your database will continue to function normally, and users can access it without interruption.

Some important points to consider:

1. After initiating a storage type change, you cannot submit another request to change the storage size, performance, or type for six hours.

2. While the change itself doesn't cause downtime, it's still recommended to perform this change during a low-traffic period to minimize any potential performance impact.

3. Monitor your instance's performance metrics before and after the change to ensure the desired outcome.

4. Ensure you have recent backups before making any changes as a best practice.

5. With GP3, you'll get a baseline performance of 3,000 IOPS and 125 MB/s throughput included in the base storage price, and you can configure additional IOPS and throughput independently if needed.

The transition from GP2 to GP3 is designed to be non-disruptive, making it safe to perform even in a production environment.
Sources
RDS Storage Type Change: Downtime for gp2 → gp3 and gp3 → gp2? | AWS re:Post
Capture and diagnose I/O bottlenecks on Amazon RDS for SQL Server | AWS Database Blog
GP2 vs GP3 RDS storage mechanics - how it works - bottleneck, metric to watch, how to purchase more | AWS re:Post