The FlashArray//XL utilizes a massive 5U chassis with a highly specific PCIe slot population architecture optimized for NVMe-oF (RDMA over Converged Ethernet - RoCE) backend connectivity. According to the FlashArray//XL Port Usage and Definitions hardware matrix, an //XL configuration supports up to two 2-port 100GbE cards explicitly dedicated to NVMe DirectFlash Shelf (DFS) connectivity.

The standard implementation procedure mandates that the primary shelf connectivity card must be installed in PCIe Slot 0 (the default slot). However, if an Implementation Engineer arrives onsite and discovers that Slot 0 is already legitimately occupied by another critical I/O card, the officially supported secondary/alternate slot for routing the backend DFS loop is PCIe Slot 6 .

Slot 5 and Slot 8 are strictly reserved for frontend host I/O connectivity (such as 32G/64G Fibre Channel HBAs). By installing the 100GbE RoCE backend expansion card into Slot 6, the engineer ensures optimal NUMA node alignment, prevents frontend/backend traffic collisions, and passes the array's mandatory pre-flight hardware_check.py validation script, allowing the new DirectFlash Shelf to initialize seamlessly.