Which CD is essential for Vault installation?

The essential CD for Vault installation is the Operator CD. During the installation of CyberArk Vault, the Operator CD is specifically designed to facilitate the setup and configuration process. It includes necessary tools, applications, and components that are critical for proper installation and functioning of the Vault. The Operator CD helps ensure that the environment is set up correctly to manage privileged accounts and sensitive information efficiently.

In the context of the other options, while the Master CD might be relevant for certain aspects of CyberArk's suite, it does not contain the same level of installation-specific resources as the Operator CD. The Backup CD is primarily used for backup and restoration purposes and is not necessary for the initial installation. Lastly, the Authentication CD serves distinct functions related to user authentication and does not play a direct role in the core installation of the Vault.

Thus, it is clear that the Operator CD is integral to successfully setting up the CyberArk Vault environment.