Azure SQL Databases is quite a big service and it is also one of the oldest. Because of these two there are a few architectural designs that you should be aware. Some of these are:
- with every SQL logical server there is a master database resource that is created. This resource is not directly managed but for example when you configure diagnostic settings on server level you need to configure those against the master database resource rather the SQL logical server
- The SKUs of Azure SQL Databases are mostly divided into DTU and vCore based. Among the vCore based we also have Hyperscale and Serverless variants. You can also have elastic pools for some SKUs and than the databases under those elastic pools inherit their SKUs. Not all Azure SQL SKUs support all of the features of the service. Some of the features that may not be available or have some limitations across different SKUs are:
- Zone redundancy
- Hybrid benefit
- Read replicas
- Failover Group support – for example not supported on Hyperscale SKUs and supported on Serverless SKUs only auto pause delay is disabled
- Geo replication
- Short term backup
- Long term backup
Among these we also have Datawarehouses (now known as Azure Synapse Analytics) which underneath are the same resource as Azure SQL databases but have completely different options.