The explanation is that shielded instances are VM instances that have additional security features to protect them from low-level threats, such as rootkits and bootkits that can infect the firmware and operating system and are difficult to detect. Shielded instances use verified boot, which ensures that only trusted software components are executed during the boot process. Shielded instances also use virtual trusted platform module (vTPM), which provides a secure storage for encryption keys and certificates. Shielded instances are available for Oracle Linux 8 platform images with VM.Standard2.* shapes.

Oracle Security Zones is a service that helps you enforce best practices and prevent misconfigurations on your OCI resources by applying predefined policies and controls. Some of the benefits of using Security Zones are:

• Encrypt storage resources with a customer-managed key: Security Zones require that all storage resources, such as block volumes, boot volumes, file systems, and object storage buckets, are encrypted with a customer-managed key from Vault. This ensures that you have full control over the encryption and decryption of your data at rest.
• Deny public access to OCI resources, such as databases and object storage buckets: Security Zones prevent you from creating or updating OCI resources that have public access enabled, such as databases and object storage buckets that are accessible from the internet. This reduces the risk of unauthorized access or data leakage.

Exadata Virtual Machine is not a valid option for an OCI compute shape. Exadata Virtual Machine is a deployment option for Exadata Cloud Service or Exadata Cloud@Customer, which are services that provide dedicated Exadata infrastructure for running Oracle databases in OCI. Exadata Virtual Machine allows you to create multiple virtual machines on each Exadata compute node and isolate them from each other using Oracle VM technology. The valid options for OCI compute shapes are:

• Bare Metal: A bare metal instance is a physical server that gives you direct access to the underlying hardware and full isolation from other tenants.
• Dedicated Virtual Machine Host: A dedicated virtual machine host is a physical server that hosts only your virtual machine instances and no other tenant’s instances.
• Virtual Machine: A virtual machine instance is a virtual server that runs on a shared physical server with other tenants’ instances.
• Burstable: A burstable instance is a virtual machine instance that has a baseline utilization of either 12% or 50% of each CPU core and can burst above the baseline when needed.