On hard drives, even SATA ones this is mostly sorted out since a few years (Linux doesn't use FUA over SATA, leaves write-back drive cache enabled, and just iss

On hard drives, even SATA ones this is mostly sorted out since a few years (Linux doesn't use FUA over SATA, leaves write-back drive cache enabled, and just issues a full cache flush, which the big majority of drives respect, more or less). SSDs, less so, fsync is a rather relative affair on some of them. IMHO, from having spent a fair amount of time on this, durability is a "fluid" concept, especially on desktop hardware (Microsoft had the right idea when they built Win Update on TxF), so if the data is important enough to worry about it, you should architect the system in a way that the durability of a fildes or drive is irrelevant to the overall system.