FlashArray//XL architectures offer the ability to leverage DirectMemory Modules (DMMs) to drastically accelerate read-intensive workloads. DMMs are specialized drives built on Storage Class Memory (SCM) technologies, such as Intel Optane. They act as a high-speed read cache tier, sitting seamlessly between the array's ultra-fast NVRAM (which handles incoming writes) and the standard DirectFlash Modules (which provide the bulk capacity).
Because the entire purpose of a DirectMemory Module is to provide the absolute lowest read latency possible, physical proximity to the controller's CPUs and direct access to internal PCIe lanes is mandatory. Therefore, DMMs must be installed directly into the primary FlashArray chassis in specifically designated slots.
Installing DMMs into an external DirectFlash Shelf (DFS) is strictly prohibited and physically unsupported.
Routing read-cache traffic across an external NVMe-oF (RoCE) backend fabric-even at 100GbE speeds- would introduce microsecond latency overheads that completely defeat the performance benefits of Storage Class Memory. Furthermore, DMMs share the exact same physical U.2/NVMe drive slot form factor as standard capacity DFMs (making Option C false), and they are supported across multiple array models beyond just the //XL 170 (making Option B false). An Implementation Engineer must strictly validate the chassis population rules before inserting DMMs to ensure the system recognizes the cache tier correctly upon initialization.