-If there is a data center outage or power outage, both vPC peers consisting of Nexus 7000 Switches are down. Sometimes, only one of the peers can be restored. Since the other Nexus 7000 is still down, vPC peer-link as well as vPC peer-keepalive link are also down. In this scenario, vPC will not come up even for the Nexus 7000 which is already up. We have to remove all vpc configurations from the port-channel on that Nexus 7000 to get the port-channel working. When the other Nexus 7000 comes up then we have to again make configuration changes to include the vpc configuration for all vPC. Starting with 5.0(2), to take care of this behavior Cisco added configuring reload restore command under vpc domain configuration.
-If for some reason vPC peer-link goes down. Since vPC peer-keepalive is still up, vPC secondary peer device brings down as well all of its vPC member ports due to dual active detection. Hence all the traffic goes through vPC primary switch. Then for some reason, vPC primary switch also goes down. This will blackholed the entire traffic since vPC on secondary are still down because it had detected dual active detection before the vPC primary switch went down.
Cisco merged these two enhancements/features together into one feature starting from 5.2(1) called vPC auto-recovery.