I've somewhat researched the topic of "durability + harddisks/SSDs" for a while since I was interested in writing a simple Key-Value store. The simple answer i

I've somewhat researched the topic of "durability + harddisks/SSDs" for a while since I was interested in writing a simple Key-Value store. The simple answer is that "fsync" is basically the best option you have. The hardware controller tells the OS "sure, I've written all this" and the OS has no real mechanism to verify this. Worse even, some cheaper SSDs an HDDs do reorder writes around fsync's, in one case a bad HDD was able to corrupt ZFS(!) (reproducible) when loosing power during a write. The fun thing is also that filesystems themselves aren't much better either. Ext4&co. sometimes don't propagate write errors at all, so in the remote event that the HDD controllers lowers itself down the plebian OS to tell it that it may have lost a byte or gigabyte, the filesystem is probably going to ignore it since the write was already buffered and fsync'd. The only real reason why computers aren't spontaneously combusting is that most HDDs and SSDs don't do this, even in consumer space and an unexpected loss of power is rare to also meet some critical write. (ext4's physical journaling also helps a lot to make it resistant) If you want a full taste of how it works out, get a Raspberry Pi, load in a super cheap microSD and unplug the power a couple times while running a browser or other disk-heavy load.