ext4 vs fsync, my take

“It should be noted that POSIX, and even ext4 gives no
guarantees that the file will survive a system crash even if using
fsync. For instance, the data could be outstanding in hardware
buffers when the crash happens, or the filesystem in use may not be
journaled or otherwise be robust wrt crashes. However, in case of a
filesystem crash it gives a much better chance of getting the new
data rather than the old, and on reordering filesystems like an
unpatched ext4 it avoids truncated files from the rename
method.

“Both the fsync and the non-fsync version has their places. For
very important data the guarantees given by fsync are important
enough to outweight the disadvantages. But in many cases the
disadvantages makes it too heavy to use, and the possible data loss
is not as big of an issue (after all, system crashes are pretty
uncommon).”

Complete
Story