The physical installation of a Pure Storage FlashArray chassis begins by defining the bottom boundary of the allocated rack space. The installation rails are aligned with the bottom edge of the lowest designated Rack Unit (RU). To secure the rail correctly, a cage nut is installed in the lowest square hole of this lowest RU. This serves as the primary reference point for mounting the rail and ensuring the entire chassis is positioned accurately within the rack. While other cage nuts are installed, this is the foundational starting point.

B. Lowest square of top RU: This location is used for an upper attachment point on the rail, not the primary alignment point which is established at the bottom.

C. Top square of the lowest RU: This is a secondary attachment point for the rail bracket; the lowest square hole is the primary point for aligning the rail's bottom edge.

1. Pure Storage. (2023). FlashArray//X and FlashArray//C R4 Hardware Installation Guide. Document P/N 30-0353-04. Section: "Install the Rails", subsection "Install Cage Nuts". The diagrams (e.g., Figure 11) visually confirm that a cage nut is placed in the bottom-most hole of the lowest RU that the chassis will occupy.

2. Pure Storage. (2022). FlashArray//XR3 Installation and Upgrade Guide. Document P/N 30-0333-04. Section: "Install the Rails", subsection "Install Cage Nuts". The guide states, "For each of the four rack posts, install two cage nuts in the top and bottom square holes of the 3U space reserved for the chassis." This procedure explicitly includes installing a cage nut in the bottom square hole of the lowest RU.