Switch fabric modules
The switch fabric modules play a dual role in the fabric connectivity between line cards, providing both the data-plane connectivity and the control-plane connectivity needed for end-to-end credit management in each of the line cards.
In each chassis model, two slots are designated for supporting the control-plane connectivity. In the Brocade VDX 8770-4, the slots S1 and S2 are the designated control-plane slots. In the Brocade VDX 8770-8, the slots S3 and S4 are the designated control-plane slots. At least one of the control-plane slots must be populated to maintain operation. If you remove the switch fabric modules from both the control-plane slots, all line cards will be faulted and the chassis is no longer operational.