Azure SQL Database and Data Warehouse offer encryption-at-rest by providing Transparent Data Encryption (TDE) for all data written to disk, including databases, log files and backups. This protects data in case of unauthorized access to hardware. TDE provides a TDE Protector that is used to encrypt the Database Encryption Key (DEK), which in turn is used to encrypt the data. With the TDE and Bring Your Own Key (BYOK) offering currently in preview, customers can take control of the TDE Protector in Azure Key Vault.
Taking advantage of TDE with BYOK for databases that are geo-replicated to maintain high availability requires to configure and test the scenario carefully.