Understanding the strict hardware boundaries of Pure Storage capacity expansion is critical. DirectFlash Modules (DFMs) and DirectFlash Modules with Distributed NVRAM (DFMDs) are fundamentally different hardware components. Standard DFMs contain only raw NAND flash and rely entirely on centralized, dedicated NVRAM modules located in the array chassis to protect write cache. DFMDs, however, feature their own onboard non-volatile memory to distribute the cache load across the capacity drives (primarily utilized in //XL and //XR4 architectures).

Pure Storage architecture explicitly dictates that drives operating within a single efficiency bundle or Wide Write Group (WWG) must be of the exact same hardware classification to ensure predictable parity calculation, wear leveling, and cache distribution. Mixing legacy DFMs with newer DFMDs within the same 20-module write group creates a severe hardware imbalance and is a strictly unsupported configuration.

While internal engineering tunables (like those suggested in Option A) occasionally exist to force overrides in lab environments, applying them in a customer's production array to bypass physical hardware incompatibility violates all implementation best practices. The only correct and safe action for the Implementation Engineer is to halt the physical installation, flag the Bill of Materials (BOM) mismatch, and work with the account/logistics team to RMA the DFMDs and ship the correct standard DFMs.