The RAID level that will yield the best combination of available space and redundancy, given the setup with two mirrored drives for the operating system and three remaining drive bays for storage, is RAID 5.
RAID 5 provides a good balance of redundancy and storage efficiency. It uses striping with distributed parity, which means that data and parity information are spread across all the drives.
With three drive bays, RAID 5 will provide redundancy (protection against a single drive failure) while maximizing usable storage space.

If users cannot access a new server by name, but the server does respond to a ping request using its IP address, it means that there is a problem with name resolution. The DNS (Domain Name System) is a service that maps hostnames to IP addresses and vice versa. Therefore, the best step to perform next is to examine the DNS to see if the new server record exists and matches its IP address. If not, the DNS record needs to be added or updated accordingly.
Running the tracert command from a workstation would not help with name resolution, as it only shows the route taken by packets to reach a destination by IP address. Correcting the missing DHCP scope would not help either, as DHCP (Dynamic Host Configuration Protocol) only assigns IP addresses and other network settings to clients, but does not resolve names. Updating the workstation hosts file would be a temporary workaround, but not a permanent solution, as it would require manually editing every workstation's hosts file with the new server's name and IP address.

The administrator should rebuild the volume to restore it after replacing the failed hard drive. A volume is a logical unit of storage that can span across multiple physical disks. A volume can be configured with different levels of RAID (Redundant Array of Independent Disks) to provide fault tolerance and performance enhancement. When a hard drive in a RAID volume fails, the data on that drive can be reconstructed from the remaining drives using parity or mirroring techniques.
However, this process requires a new hard drive to replace the failed one and a rebuild operation to copy the data from the existing drives to the new one. Rebuilding a volume can take a long time depending on the size and speed of the drives and the RAID level.

A security guard is a human element in physical security, making them susceptible to social engineering attacks. Social engineering exploits human behavior, and a guard can be tricked into allowing unauthorized access through persuasion, manipulation, or deception.