Fault Tolerance Practice Test

A home security company monitored sensors over a wireless network. Sometimes interference flipped bits in a message, so the system added a small check value to each packet. If the check did not match, the receiver requested the packet again, and the correct alert was delivered. This kept door and window events accurate even on noisy nights. In the example given, how does the described system maintain functionality during a failure?

A cloud storage service ran on a primary server and a backup server in different data centers. When the primary server crashed during peak use, the system automatically switched users to the backup within seconds, and most people kept uploading files without noticing. The service logged the failure and later repaired the primary server, then restored it as the main system. Based on the scenario described, in the scenario, what role does Failover play?