Which type of backup is required to ensure a server OS and data can be fully recovered after simultaneous hard disk failures?

In the context of recovering a server OS and data after simultaneous hard disk failures, a bare metal backup is the most appropriate choice. A bare metal backup captures a complete image of the entire system, including the operating system, applications, and all data, in a way that allows for a full restoration to a different hardware environment if necessary.

This is essential because, in the event of hard disk failures, simply having data files might not be sufficient; the system needs to be restored to its previous operational state, which includes restoring the operating system and configurations. A bare metal backup allows for this level of recovery because it encompasses everything required for a complete system restoration.

Other types of backups, such as full, differential, and incremental, may involve backing up data files or changes to files but do not inherently include the full operating system and system configuration settings in a way that supports a complete rebuild after a catastrophic failure like multiple hard disk failures. These backups may be effective for protecting data or recovering from singular file loss but fall short of ensuring a complete and efficient recovery in the scenario described.