"Force Unit Access" (FUA) is an I/O write command option that forces written data all the way to stable storage.FUA write commands (WRITE DMA FUA EXT 3Dh, WRITE DMA QUEUED FUA EXT 3Eh, WRITE MULTIPLE FUA EXT CEh), in contrast to corresponding commands without FUA, write data directly to the media, regardless of whether write caching in the device is enabled or not.