These are two methods that can prevent a user from installing an OS on a server if properly configured. A bootloader password is a password that protects the bootloader from unauthorized access or modification. The bootloader is a program that loads the operating system into memory when the system boots up. If a user does not know the bootloader password, they cannot change the boot order or boot from another device such as a CD-ROM or USB drive that contains an OS installation media. A BIOS/UEFI password is a password that protects the BIOS (Basic Input Output System) or UEFI (Unified Extensible Firmware Interface) from unauthorized access or modification. The BIOS or UEFI is a firmware that initializes and configures the hardware components of the system before loading

RAID 6 is a type of RAID that uses block-level striping with two parity blocks distributed across all member disks. It allows for two disk failures within the RAID set before any data is lost1. A minimum of four disks is required to create RAID 61. To increase the size of an existing RAID 6 array, the administrator can replace the array drives one at a time with larger drives and then expand the array. This way, the data and parity are rebuilt on each new drive and the array remains operational during the process2.

A sniffer is a tool that captures and analyzes network traffic on a subnet or a network interface. It can help identify the source, destination, protocol, and content of the traffic and detect any anomalies or issues on the network. Verified References: [Sniffer], [Network traffic]

The correct answer is D. per-core.
The per-core licensing model was created by software companies in response to the increasing density of processors. This model is used for software that runs on servers with multi-core processors, and the licensing fee is based on the number of cores. This way, the software vendors can charge more for software that runs on servers with more processing power1

The concept in use when dual power supplies are connected to different power sources is fault tolerance. Fault tolerance is the ability of a system to continue operating without interruption or loss of data in the event of a failure of one or more components. By connecting dual power supplies to different power sources, the system can switch to the alternative power supply or source if one fails, ensuring continuous availability and reliability.
References: CompTIA Server+ SK0-005 Certification Study Guide, Chapter 1, Lesson 1.3, Objective 1.3