The FlashArray//X architecture is fundamentally designed around a modular, common chassis that supports multiple generations of controllers. This design is a core tenet of Pure Storage's Evergreen architecture. When upgrading from an //XR2 to an //XR3 model, the existing 3U chassis, power supplies, and flash modules remain in place. The upgrade is performed by non-disruptively swapping the older //XR2 controller modules with the new //XR3 modules, one at a time. This eliminates the need for a "forklift" upgrade or data migration, dramatically simplifying the process both physically and logically.

B. InfiniBand connectivity between controllers: This is the high-speed internal interconnect for high availability in all modern FlashArray models; it is not a specific design choice that simplifies the upgrade between generations.

C. NVRAM modules in both controllers: NVRAM is a standard, critical component for write caching and power-loss protection in all FlashArray controllers, not an architectural feature that simplifies the physical upgrade process.

D. Re-use of existing HBAs to prevent WWN changes: Host Bus Adapters (HBAs) are integrated components of the controller module. Therefore, they are replaced during a controller upgrade, not re-used. The Purity software manages WWN persistence to minimize host-side changes.

1. Pure Storage, Inc. (2021). FlashArray//X Hardware Guide. Section: "FlashArray//X Chassis". This guide details the common 3U chassis used across different //X generations (R2, R3, R4), illustrating that the chassis is a persistent component while controllers are modular and swappable. The upgrade path relies on this shared physical platform.

2. Pure Storage, Inc. (2022). White Paper: An Introduction to Evergreen Storage. Page 4, Section: "Upgrade Flex". This document explicitly states, "With Upgrade Flex, you can modernize your controllers to the latest generation, any time, within the same chassis. This means no downtime, no performance impact, and no data migration." This directly supports the concept of a common chassis simplifying controller upgrades.