An incremental backup is a backup method that only backs up the files that have changed since the last backup, whether it was a full or an incremental backup. An incremental backup can save disk space and time, as it only copies the new or modified data. An incremental backup can also improve the RTO (Recovery Time Objective), which is the maximum acceptable time to restore data after a disaster. This is because an incremental backup can restore data faster than a full or a differential backup, as it only needs to apply the latest changes to the previous backup1.

A differential backup is a type of backup that copies all the files that have changed since the last full backup.
A differential backup requires more storage space than an incremental backup, which only copies the files that have changed since the last backup of any type, but it also requires less time to restore in case of data loss. By combining a full, weekly backup with daily differential backups, the administrator can ensure that only two backup sets are needed to restore a full backup as quickly as possible. Verified References: [Incremental vs Differential Backup]

To comply with the user requirements, the best options are to install the OS on a RAID 1 array, configure RAID 5 for the application data, and use SSD hard drives for the data application array. Here is why:
RAID 1 is a mirroring technique that creates an exact copy of data on two disks. This provides redundancy and fault tolerance in case of hard drive failure. RAID 1 also improves read performance since either disk can be read at the same time. Therefore, installing the OS on a RAID 1 array meets the first requirement of separating the OS from the application data and protecting it from hard drive failure.
RAID 5 is a striping technique with parity that distributes data and parity blocks across three or more disks. This provides improved performance and storage efficiency compared to RAID 1, as well as fault tolerance in case of a single disk failure. Therefore, configuring RAID 5 for the application data meets the second and third requirements of providing high IOPS performance and data availability.
SSD hard drives are solid-state drives that use flash memory to store data. They have no moving parts and offer faster read and write speeds, lower latency, and lower power consumption than traditional HDDs. Therefore, using SSD hard drives for the data application array meets the second requirement of providing high IOPS performance.
References:
https://phoenixnap.com/kb/raid-levels-and-types
https://en.wikipedia.org/wiki/Standard_RAID_levels

The command that the administrator should issue to configure MySQL successfully is setenforce 0. This command sets the SELinux (Security-Enhanced Linux) mode to permissive, which means that SELinux will not enforce its security policies and will only log any violations. SELinux is a feature that provides mandatory access control (MAC) for Linux systems, which can enhance the security and prevent unauthorized access or modification of files and processes. However, SELinux can also interfere with some applications or services that require specific permissions or ports that are not allowed by SELinux by default. In this case, MySQL may not be able to run properly due to SELinux restrictions. To resolve this issue, the administrator can either disable SELinux temporarily by using setenforce 0, or permanently by editing the /etc/selinux/config file and setting SELINUX=disabled. Alternatively, the administrator can configure SELinux to allow MySQL to run by using commands such as semanage or setsebool.
Reference:
https://blogs.oracle.com/mysql/selinux-and-mysql-v2

The correct answer is D. A virtual switch.
A virtual switch is a software-based network device that connects the virtual machines (VMs) in a virtual environment and allows them to communicate with each other and with the physical network. A virtual switch can also create and manage virtual LANs (VLANs), which are logical segments of a network that separate the traffic of different VMs or groups of VMs. A VLAN needs a DHCP server to assign IP addresses to the VMs that belong to it. A virtual switch can act as a DHCP relay agent and forward the DHCP requests from the VMs to the DHCP server on the physical network. This way, the VMs can receive correct IP addresses for their VLANs123 A virtual router is a software-based network device that routes packets between different networks or subnets.
A virtual router can also create and manage VLANs, but it is not necessary for a VM to receive a correct IP address. A virtual router can be used to provide additional security, redundancy, or load balancing for the VMs12 A host NIC is a physical network interface card that connects the host machine to the physical network. A host NIC can also support VLAN tagging, which allows the host machine to communicate with different VLANs on the network. However, a host NIC alone cannot ensure that a VM receives a correct IP address for its VLAN. The host NIC needs to be connected to a virtual switch that can relay the DHCP requests from the VMs to the DHCP server12 A VPN is a virtual private network that creates a secure tunnel between two or more devices over the internet.
A VPN can be used to encrypt and protect the data traffic of the VMs, but it is not related to the configuration of VLANs or IP addresses. A VPN does not affect how a VM receives a correct IP address for its VLAN14 A vNIC is a virtual network interface card that connects a VM to a virtual switch or a virtual router. A vNIC can also support VLAN tagging, which allows the VM to communicate with different VLANs on the network.
However, a vNIC alone cannot ensure that a VM receives a correct IP address for its VLAN. The vNIC needs to be connected to a virtual switch or a virtual router that can relay the DHCP requests from the VMs to the DHCP server12