The correct pre-implementation step is to make space in the rack where the chassis is located.
Cabling Standards: DirectFlash Shelves (DFS) connect to the FlashArray via RoCE (RDMA over Converged Ethernet) using QSFP28 cables. The standard cabling kits provided by Pure Storage typically include short-range Passive DACs (e.g., 1m to 3m) or short Active Optical Cables (AOCs).
Distance Constraint: A distance of 6 meters between racks usually exceeds the length of standard included cables and introduces complexity regarding cable management, signal integrity, and "span" policies. While custom long-range optical cables exist, they are not standard stock and relying on ordering a non-standard "7m" cable (Option B) is a risk.
Best Practice: Pure Storage installation guides explicitly recommend installing expansion shelves in the same rack and contiguous to the controller chassis whenever possible. This ensures optimal airflow, ease of serviceability, and adherence to standard cabling schematics. Moving the entire controller chassis (Option C) is a disruptive and heavy-lift operation, whereas clearing 3U of space (Option A) is the standard facility preparation task required for a successful deployment.