An access control vestibule is a physical security concept that limits personnel access to a restricted area within a data center. It is a small room or hallway that has two doors: one that leads to the outside and one that leads to the restricted area. The doors are controlled by an electronic lock that requires authentication, such as a card reader, biometric scanner, or keypad. Only authorized personnel can enter the vestibule and access the restricted area. Reference: CompTIA Server+ Certification Exam Objectives, Domain 5.0: Security, Objective 5.1: Given a scenario, apply physical security methods to a server.

Explanation
If the server is not reachable by name but can be accessed by IP address, it means that there is a problem with name resolution. The hosts file and the DNS server are both responsible for mapping hostnames to IP addresses. Therefore, the server administrator should check these two files for any errors or inconsistencies that might prevent the server from being resolved by name. References:
https://www.howtogeek.com/662249/how-to-edit-the-hosts-file-on-linux/
https://www.howtogeek.com/164981/how-to-use-nslookup-to-check-domain-name-information-in-microsoft-win

The backplane is a circuit board that connects multiple hard drives to a RAID controller and provides power and data transfer between them. If the backplane has failed, it may cause all the hard drives to be offline and prevent the server from booting into the OS. The fact that replacing one of the drives with a known-good drive did not work, and that taking a drive out of the server and placing it in a spare server made it functional, suggests that the problem is not with the drives themselves but with the backplane. A corrupt kernel (A) would not affect the status of the hard drives, as it is a software component of the OS. Resource misallocation (B) would not cause all the hard drives to be offline, as it is a configuration issue that affects how resources are assigned to processes or applications. Reseating the drives (D) would not help, as it would not fix a faulty backplane. References: https://www.dell.com/support/kbdoc/en-us/000130114/how-to-troubleshoot-a-faulty- backplane

Explanation
The most likely cause of the issue is that the server has not been joined to the domain. A domain is a logical group of computers and devices that share a common directory service and security policy. A domain controller is a server that manages the domain and authenticates users and computers that want to access domain resources. To log on with domain credentials, a server must be joined to the domain and registered in the directory service. If a server has not been joined to the domain, it will not be recognized or authorized by the domain controller.
References: CompTIA Server+ SK0-005 Certification Study Guide, Chapter 4, Lesson 4.3, Objective 4.3

Explanation
A warm site is a type of disaster recovery site that has a target storage array that receives replication traffic and servers that are only powered on in the event of a disaster. A warm site is a compromise between a hot site and a cold site. A warm site has some equipment and data ready, but requires some configuration and restoration before resuming operations. A warm site is usually located in a different geographic area than the primary site and has redundant power, cooling, network, and security systems. A warm site is suitable for organizations that can tolerate some downtime and data loss in case of a disaster. A cloud site is a type of disaster recovery site that uses cloud-based resources and platforms to store backups and restore data and applications after a disaster. A cold site is a type of disaster recovery site that has only basic infrastructure and space available, but requires significant setup and installation before resuming operations. A hot site is a type of disaster recovery site that has all the equipment and data ready to resume operations as soon as possible after a disaster.
References: https://www.techopedia.com/definition/11172/hot-site
https://www.techopedia.com/definition/11173/warm-site
https://www.techopedia.com/definition/11174/cold-site
https://www.techopedia.com/definition/29836/cloud-recovery