Comment by gizmo686

What if the hardware has its own notion of sync. I am not familiar with disk IO protocols, but I assume they are permitted to store writes in an internal buffer. In such a case, I would expect fsync to issue a sync request to the device and wait until the device reports that the sync is finished. Admittedly, the phrasing of the spec is not 100% clear on this point; but I think the correct reading of it is that the correct behavior is to wait until the device actually commits the data (or at least claims to; at some point broken/lieing hardware is just broken).