Ext4 filesystem hits Android, no need to fear data loss (ars technica)

My model can't really fail to be accurate, since it includes the possibility of arbitrary deviations from the predicted outcome. And, actually, nothing is safe at all; your storage medium might fail, your video driver might scribble over your disk or your dirty pages, your hard drive might read garbage out of memory losing power and write it with the power left in its capacitors. I actually suspect that, based on the model I stated, a more common and more extensive source of differences from some potential snapshot is things that syncing couldn't have helped with than things that syncing could have helped with (with the exception of ext4 having a particularly common and obvious divergence).

There's also been not that long in the UNIX tradition when you could be reasonably confidant that a power failure shortly after you changed something in a directory wouldn't trash other things in the directory, making it kind of irrelevant whether you'd called fsync on the directory to make sure that the disk was correct before it got corrupted.

In general, there's a tradeoff among filesystem complexity, slowness, and
deviation from non-crash state. None of these go to zero without making the others terrible, even if you call sync all the time.

(In fact, my model does require an fsync when moving a file by copying it, at least across directories; the snapshotting process could read the destination directory before you write the file and the source directory after you unlink it.)