The T11 fiber committee changed the FC-PI-3 standard for 8G FC. This change uses the ARB(FF) primitive signal in place of IDLE as a fill word to maintain link synchronization. However, this would not be the case with 4G and slower links which would still use IDLE primitives as the fill word. So, when Brocade introduced the 8G FC platforms (DCX, DCX 4-S, 300, 5100, 5300, etc….) it became necessary to be able to offer up the ability to select which one to use. The portcfgfillword CLI command is used to perform this switch. For Brocade 8G platforms running FOS v6.3.1 or higher, configuring the fill word to mode 3 typically enables the port to use the right combination of Fibre Channel primitives to fully interoperate with the attached end devices. However, if a device is known to require mode 2 (IDLE/ARB) then configuring mode 2 on the 8G switch port will activate the link sooner. If mode 3 is used in this environment, then the port will first attempt mode 1 (ARB/ARB) then eventually settle to mode 2 which will cause a delay in initializing the port.
Portcfgfillword mode selections:
Mode 0 - Sets IDLE mode in the Link Init and IDLE as the fill word (default).
Mode 1 - Sets ARB(ff) in the Link Init and ARB(ff) as the fill word.
Mode 2 - Sets IDLE mode in the Link Init and ARB(ff) as the fill word.
Mode 3 - Attempts hardware arbff-arbff (mode 1) first. If the attempt fails to go into active state, this command executes software idle-arb (mode 2).
NOTE: The above does not apply to the 16G FC platforms (DCX8510-8, 8510-4, 6505, 6510, 6520, etc…). This includes 16G platforms with 8G SFPs in them (thus making them 8G however they remain 16G capable).