Which of the following is not a common control that focuses on availability?

Disk encryption is not a common control that specifically focuses on availability. Instead, disk encryption primarily serves to protect the confidentiality and integrity of data by encoding the information stored on a disk. Its primary function is to prevent unauthorized access to sensitive information, ensuring that only those who have the decryption key can access the data. While encryption contributes to data protection and security, it does not actively enhance system availability or ensure that services remain accessible.

In contrast, controls like redundant servers, load balancers, and backup power supplies are directly aimed at improving system availability. Redundant servers provide failover capabilities to keep services running in case of a server failure, load balancers distribute traffic across multiple servers to optimize resource use and prevent overload, and backup power supplies ensure that systems remain operational even during power outages. All of these mechanisms work to maintain continuous access to services and resources, which is the core objective of availability-focused controls.