This CucsFabricFillPattern field records which idle-time fill pattern is configured on the Fibre Channel link underlying this direct-attached FC storage port. For one physical FC port on the fabric interconnect that is a member of a direct-attached (non-SAN-switch) external storage connection, FC links transmit filler words (such as IDLE or ARB sequences, historically tied to Fibre Channel Arbitrated Loop) between real frames, and getting this setting wrong relative to what the storage array or switch on the other end expects is a known cause of an FC link that trains up but then throws CRC errors. Most modern point-to-point FC links leave this at the 'idle' fill pattern; 'arbff' would only be expected on legacy arbitrated-loop-style connections.