To answer this question, we need to understand the concept of vertical scalability.
Vertical scalability refers to the ability to increase the capacity of a single server or resource within a system, such as memory, CPU, or storage. Let's go through each option to determine which ones are true about vertical scalability:
A. Achieved by adding servers to the system - This statement is incorrect. Adding servers to the system is known as horizontal scalability, not vertical scalability.
B. Achieved by adding capacity (memory, CPU and so on) - This statement is correct. Vertical scalability is achieved by adding capacity to a single server or resource within a system, such as increasing memory or CPU.
C. It is generally more expensive than horizontal scaling - This statement is not mentioned in the options, so we cannot determine its truthfulness.
D. Decreases manageability - This statement is incorrect. Vertical scalability does not necessarily decrease manageability. It may introduce some complexities, but it does not inherently decrease manageability.
E. Requires few or no changes to the system architecture - This statement is correct. Vertical scalability typically requires minimal changes to the system architecture. It focuses on enhancing the capabilities of individual resources rather than restructuring the entire system.
F. Has little or no impact on the reliability and availability of the system - This statement is correct. Vertical scalability does not have a significant impact on the reliability and availability of the system. It primarily focuses on increasing capacity and performance without affecting the overall reliability.
Based on the explanations above, the correct options are B, E, and F.