Azure SQL Managed Instance has predefined storage space that depends on the values of reserved storage and vCores that you choose when you provision the instance. In this post you will see how to monitor storage space on the Managed Instance. In Managed Instance you can reach three storage limits: Storage limit of managed instance... Read more

https://blogs.msdn.microsoft.com/sqlserverstorageengine/2019/03/08/monitor-storage-local-storage-usage-on-general-purpose-managed-instance/