Compute
Fabric interconnects and service profiles
Cisco UCS centralizes management in the Fabric Interconnect (FI) pair. In end-host mode (the default) the FIs do not run STP and behave like hosts toward upstream switches, with uplinks trunking all required VLANs. LAN and SAN sides can be configured in disjoint (separate) mode; in disjoint mode, server ports on the SAN fabric cannot carry LAN traffic, and vice versa.
Everything logical is abstracted into pools - MAC, WWNN/WWPN, UUID, server, IP - and combined into a service profile that is associated with a blade or rack server. Boot order, BIOS, firmware, vNIC/vHBA placement, and local disk policies live inside the profile, so a change requires re-association (or a policy update plus reboot) to take effect.
Fabric failover
A vNIC with fabric failover has an active path on its pinned fabric and fails over to the peer if the pinned path dies. If the peer FI has lost its uplinks, traffic cannot pass; disable failover for workloads needing strict per-fabric isolation.
Traps
Do not confuse server ports (to servers/IO modules), LAN uplink ports, and FCoE or SAN uplink ports - roles are not freely interchangeable. B-series blades appear only after chassis discovery over the port channel.
Rule of thumb
If a setting is not in a policy, it will not survive re-association. Put every manual CLI change into a service profile policy, or it silently disappears on the next association.