A full interruption test is the most realistic and reliable way to ensure that recovery time objectives (RTOs) are met for an organization's disaster recovery plan (DRP). RTOs are the maximum amount of time that a business can tolerate being offline after a disaster. A full interruption test involves shutting down the primary site and switching over to the backup site, simulating a real disaster scenario. This test can measure the actual time it takes to restore the systems, applications, and functions that are critical for the business continuity. A full interruption test can also reveal any issues or gaps in the DRP that might affect the recovery process.
The other options are not as effective as a full interruption test for ensuring RTOs are met. A cyber resilience test is a type of DR test that focuses on the ability to withstand and recover from cyberattacks. It does not necessarily cover other types of disasters or test the entire DRP. A tabletop test is a low-impact DR test that involves a walkthrough of the DRP with the key stakeholders and staff. It does not involve any actual switching over or testing of the backup systems. A parallel test is a type of DR test that involves running the backup systems alongside the primary systems, without disrupting the normal operations. It does not measure the time it takes to switch over or resume operations at the backup site.
References:
Best Practices For Disaster Recovery Testing
Disaster recovery testing
Disaster Recovery Testing: Everything to Know

The best way to enforce the principle of least privilege on a server containing data with different security classifications is to apply access controls determined by the data owner. The principle of least privilege states that users should only have the minimum level of access required to perform their tasks. The data owner is the person who has the authority and responsibility to classify, label, and protect the data according to its sensitivity and value. The data owner can define the access rightsand permissions for each user or role based on the data classification policy and the business needs. This will ensure that only authorized and appropriate users can access the data and prevent unauthorized or excessive access that could compromise the confidentiality, integrity, or availability of the data. References:
* CISA Review Manual (Digital Version)
* CISA Questions, Answers & Explanations Database