The FlashArray//E (and the //XR4/R5 family) utilizes a modern architecture that moves away from the dedicated NVRAM modules found in legacy generations (like the //XR2 and //XR3). In those older systems, NVRAM was housed in specific PCIe cards plugged into the chassis.
In the FlashArray//E architecture, the Non-Volatile RAM (write buffer) functionality is Distributed directly onto the storage media itself. These specialized drives are called DFMDs (DirectFlash Modules with Distributed NVRAM).
By integrating the NVRAM into the DFMs, the array scales its write buffer cache linearly with capacity and removes the bottleneck of fixed NVRAM slots in the chassis. This allows for higher density and simplified hardware designs. During installation or inventory, engineers must distinguish between standard DFMs (which store data only) and DFMDs (which store data and act as the write cache), ensuring the correct number of DFMDs are present to form the system quorum.
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