Yes, it's an area of research, https://www.usenix.org/system/files/conference/osdi14/osdi14-paper-pillai.pdf https://www.usenix.org/system/files/conference/osdi

Yes, it's an area of research, https://www.usenix.org/system/files/conference/osdi14/osdi14-paper-pillai.pdf https://www.usenix.org/system/files/conference/osdi14/osdi14... But in the end you should code against what posix guarantees, not what particular filesystems happen to do, because the next filesystem might use some other leeway the spec provides.