The output of the configuration shows that RAID 5 was configured properly using four 200GB drives. The approximate volume size of 400GB is correct, since RAID 5 uses one disk for parity and the rest for data.
Therefore, the usable storage capacity is three-fourths of the total capacity, which is 600GB out of 800GB.
The other RAID levels given would result in different volume sizes: RAID 0 would result in 800GB, RAID 1 would result in 200GB, and JBOD would result in an error since it does not support multiple drives in a single volume. References: https://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_5

Kerberos is a network authentication protocol that uses tickets to allow clients and servers to prove their identity to each other. Kerberos relies on accurate time synchronization between the parties involved, as the tickets have expiration dates and timestamps. If the system clock of a Linux server is off by more than five minutes from the LDAP server or the domain controller, the Kerberos authentication will fail and generate errors. A local firewall is unlikely to block authentication requests if the server can communicate over the network and is configured correctly. The users' passwords are not relevant if they are known-working LDAP credentials. The server has access to the LDAP host if it can communicate over the network and is configured correctly. References:
https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/identity_management_gui
https://www.ibm.com/docs/en/aix/7.2?topic=authentication-kerberos-time-synchronization

Disabling unneeded physical ports would prevent unauthorized devices from being connected to the server, such as an outside USB drive. Setting a BIOS password would restrict access to the boot settings and prevent unauthorized changes to the boot order. The other options would not address the risk of booting from an outside USB drive

Link aggregation is a technique that combines multiple physical network links into one logical link with higher bandwidth and redundancy. It can take advantage of all the available bandwidth of the NICs (Network Interface Cards) on the server and provide load balancing and failover capabilities for network traffic. Verified References: [Link aggregation], [NIC]

Tabletop testing is a method of reviewing a DR plan without endangering company data and with a minimal time commitment. Tabletop testing involves a simulated scenario where the participants discuss their roles and responsibilities, identify potential issues, and evaluate the effectiveness of the plan. Simulated, live, and non-production testing are methods that involve more time and resources, and may pose some risks to company data. References: [CompTIA Server+ Certification Exam Objectives], Domain 6.0: Disaster Recovery, Objective 6.3: Compare and contrast various backup techniques.