RAID 6 Disk Striping with Double Parity
The RAID 6 design distributes data across a minimum of four HDDs the same way that RAID 0 and RAID 5 do, but it also distributes parity information across two disks. The result is that a RAID 6 array can recover data even with the failure of two HDDs. Reads are quick, like RAID 5, but writes are slower due to the duplication of the parity data. It is a good general solution as long as the performance hit on write tasks is not a problem for your environment.
RAID 6 requires a minimum of four HDDs.

The reason why the Linux server is not communicating on a network is that it is configured to use DHCP on a network that does not have a DHCP server. DHCP (Dynamic Host Configuration Protocol) is a protocol that allows a client device to obtain an IP address and other network configuration parameters from a DHCP server automatically. However, if there is no DHCP server on the network, the client device will not be able to obtain a valid IP address and will assign itself a link-local address instead. A link-local address is an IP address that is only valid within a local network segment and cannot be used for communication outside of it. A link-local address has a prefix of 169.254/16 in IPv4 or fe80::/10 in IPv6. In this case, the Linux server has assigned itself a link-local address of 127.0.0.1, which is also known as the loopback address. The loopback address is used for testing and troubleshooting purposes and refers to the device itself. It cannot be used for communication with other devices on the network.

An action that the administrator should take to harden the hardware of a new server is to set a BIOS password. BIOS (Basic Input/Output System) is a firmware that initializes the hardware components and settings of a system before loading the operating system. BIOS password is a security feature that requires a user to enter a password before accessing or modifying the BIOS settings or booting up the system. By setting a BIOS password, the administrator can prevent unauthorized or malicious users from changing the hardware configuration or boot order of the server.

The action that the server administrator should take once a new backup scheme has been configured is to run a restore test. A restore test is a process of verifying that the backup data can be successfully recovered and restored to its original location or a different location. A restore test can help ensure that the backup scheme is working properly, that the backup data is valid and consistent, and that there are no errors or issues during the recovery process. A restore test should be performed periodically and after any changes to the backup configuration or environment.