Direct Flash Module

Overview

The Direct Flash Module (DFM) is Pure Storage's flash module that pairs NAND with a host-side user-space Flash Translation Layer instead of a conventional drive-firmware FTL. It uses a proprietary U.2 "long" connector that remains backward-compatible with standard U.2 slots, so the same drive bay accepts either a DFM or a conventional NVMe SSD. DFMs are exposed to the host through the Linux Ublock driver (as /dev/ubX) rather than the native NVMe interface (/dev/nvmeX), yet provide a nearly plug-and-play experience once the driver is deployed. Because the user-space FTL lets software treat the entire server as a single large SSD, DFMs enable a 16+1 cross-drive RAID configuration that reduces write amplification and P/E cycles to extend endurance. In Meta's first QLC server, DFMs ship initially at 75TB with a 150TB generation planned.