The FlashArray//XL platform features a split-chassis design with a unique PCIe bus layout compared to the standard //X series. To maintain optimal performance and redundancy, the backend connectivity for DirectFlash Shelves (DFS) must be balanced across the specific PCIe root complexes managed by the dual CPUs.
For a configuration involving multiple shelves (specifically targeting the logical shelf identifiers SH8 and SH9, which often correspond to the first pair of backend loops in an //XL deployment), the validated configuration is to use PCIe Slot 0 and PCIe Slot 6. These slots are architecturally designated for the backend NVMe-oF (RoCE) fabric cards.
Using Slot 0 (typically located on the far left) and Slot 6 (located on the right side of the chassis) ensures that the I/O load is distributed across the internal midplane and CPUs correctly. Placing cards in incorrect slots (like Slot 1 or 7, which might be reserved for host I/O or inter-controller links) can result in shelf detection failures or performance bottlenecks where one CPU is overloaded with backend traffic while the other is idle.
=========