Many storage devices guarantee that all successful DMA (e.g. O_DIRECT) writes are persisted even in the event of a power loss. This does not work on storage devices that do not offer this guarantee obviously. It also does not work if the filesystem does not support direct I/O or requires metadata updates.

This is not a new trick. It has been used in many storage engine designs to effect durability without an fsync.

Thanks, that's interesting and I wasn't aware of that. Is there a consistent way to detmine if a device offers this garuntee at runtime on Linux?