When a deduplication appliance like Dell Data Domain is used as a Veeam repository, it cannot run the Veeam Data Mover Service directly. Consequently, a gateway server is required to act as an intermediary. This gateway server runs the data mover service, processes data, and sends it to the appliance. If a dedicated gateway server is not explicitly configured during the repository setup, the Veeam backup server itself assumes this role by default. The gateway role is resource-intensive, involving tasks like data synthesis for synthetic fulls, which explains the observed increase in resource consumption on the backup server.

A. The issue described is increased resource consumption on the Veeam backup server, not a performance problem on the storage appliance itself.
B. An SSL certificate issue would likely result in connection errors or job failures, not a sustained increase in server resource utilization.
D. This statement describes a solution or a consequence (the server now needs more resources), not the root cause of the problem.

1. Veeam Backup & Replication V12 User Guide for VMware vSphere, "Gateway Server," p. 59: "For some types of backup repositories, you need to deploy a gateway server. A gateway server is a Veeam backup infrastructure component that “bridges” the backup server and the backup repository... A gateway server is required for... Deduplicating storage systems." This establishes the need for a gateway.

2. Veeam Backup & Replication V12 User Guide for VMware vSphere, "Adding Deduplicating Storage Appliances," p. 518: During the repository creation wizard, the guide states: "From the Gateway server list, select a server that will be used as a gateway server." This step confirms a gateway must be chosen. If the administrator does not select a dedicated server, the backup server is often the default choice, thus taking on the role.

3. Veeam Backup & Replication V12 Best Practices, "Gateway Server," p. 31: "The gateway server is responsible for the creation of synthetic full backups... These operations are I/O intensive, and it is recommended to use a dedicated gateway server with sufficient resources." This confirms the resource-intensive nature of the gateway role, explaining the observed issue.