On FlashArray models that use standard DFMs instead of DFMDs, which NVRAM bays are always...

Understanding the hardware architecture and proper drive population rules is critical during a Pure Storage FlashArray installation. FlashArray models generally utilize either standard DirectFlash Modules (DFMs) or DirectFlash Modules with distributed NVRAM (DFMDs).

DFMDs, primarily introduced with models like the FlashArray//XL, integrate non-volatile write caching directly into the capacity drives themselves, eliminating the need for dedicated NVRAM hardware modules. However, standard FlashArray models—such as the //X10, //X20, //X50, //X70, and //X90—use standard DFMs strictly for capacity. Because standard DFMs do not contain built-in NVRAM, these arrays rely heavily on specialized, dedicated NVRAM modules to safely acknowledge incoming writes and protect data in flight against unexpected power loss or controller failures.

To maintain absolute high availability and guarantee there is no single point of failure within the write cache, NVRAM is always mirrored across two separate physical modules. During the physical hardware installation of a non-DFMD array, the Implementation Engineer must populate the dedicated NVRAM bays located centrally on the chassis. According to official Pure Storage implementation guidelines, the primary pair of NVRAM modules must always be installed in the first two designated bays, which are explicitly labeled NVB0 and NVB1. Placing the modules in alternate or staggered bays (such as NVB0 and NVB2) violates the strict hardware population rules and will prevent the array from initializing.