1 - When I activate Zone Redundancy, I can't select which redundancy zone I want one of the nodes to be in?
No - it's a managed service. It will distribute the instances automatically for you. Refer to https://learn.microsoft.com/en-us/azure/azure-sql/managed-instance/high-availability-sla?view=azuresql for details of this implementation
2 - When I have zone redundancy in a failover with Business Critical, I cannot shut down or restart the instance?
Correct - that's expected as well. As per https://learn.microsoft.com/en-us/azure/azure-sql/managed-instance/instance-stop-start-how-to?view=azuresql&tabs=azure-powershell-prep%2Cazure-portal#limitations-of-the-stop-and-start-feature
- You can't stop instances that:
- Have an ongoing management operation (such as an ongoing restore, vCore scaling, and so on)
- Are part of a failover group
- Use the Managed Instance link
- have zone redundancy enabled
- are part of Instance pool
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hth
Marcin