The FlashArray//XR5 (and //E family) introduces a significant architectural shift regarding Non-Volatile RAM (NVRAM). In previous generations (like R2/R3), NVRAM was provided by dedicated PCIe modules installed in specific "NVB" slots in the chassis.
In the //XR5 architecture, Pure Storage moved to Distributed NVRAM . The NVRAM functionality is integrated directly into the DirectFlash Modules (specifically the DFMDs - DirectFlash Module with Distributed NVRAM). This allows the NVRAM capacity to scale with the storage and removes the bottleneck of dedicated slots.
For a system to function correctly, a minimum number of these NVRAM-equipped modules must be present to form the initial write buffer and system quorum. The standard installation requirement for an //XR5 is that the first 10 slots (Slots 0-9) are populated with these specific DFMDs. This ensures there is sufficient distributed NVRAM capacity to boot the Purity operating environment and handle incoming writes safely.
The Implementation Engineer must populate these slots first before adding standard DFMs in the remaining slots.
=========