Upgrading from a fully populated FlashArray//X90 R3 to a FlashArray//XL introduces a unique set of hardware migration challenges. To facilitate this massive transition, Pure Storage utilizes a feature called Shelf Personality Mode (SPM). In SPM, the legacy //X90 controllers temporarily act as a "dumb" NVMe-oF expansion shelf attached to the new //XL controllers, allowing the capacity drives to be transparently migrated without external swing hardware.

However, DirectMemory Modules (DMMs)—which are high-speed Storage Class Memory (SCM) drives used strictly for read caching—are handled differently than standard capacity DirectFlash Modules (DFMs). DMMs do not hold persistent, uniquely resilient user data; they hold a volatile copy of hot read blocks.

While the system is still operating in Shelf Personality Mode, the official Hardware NDU procedure dictates that the Implementation Engineer cannot simply yank the DMMs out, nor can they be migrated collectively as a "data pack." Instead, the engineer must evacuate and remove each DMM one-by-one, and set them aside . By initiating a manual evacuation on a DMM, Purity gracefully flushes the read cache mapping for that specific module. Once fully evacuated, the drive is safely removed from the legacy //X90 chassis. After the HWNDU is completely finished and the //XL is operating independently, the engineer can then re-insert those compatible DMMs into specific designated slots (typically slots 20-39) on the new //XL chassis to rebuild the cache tier.