Your OS or filesystem may maintain a blacklist of lying devices (IIRC XFS does so), although such probably isn't exported to the user. Regardless, those blackl

Your OS or filesystem may maintain a blacklist of lying devices (IIRC XFS does so), although such probably isn't exported to the user. Regardless, those blacklists are built via testing, and probably aren't comprehensive. If you absolutely positively must be assured your write is persisted, I recommend fsync, sync, waiting five minutes, fsync and sync again, then top it off with a prayer.