The OS can't do anything. The Controller says "Fsync? Sure thing." and that's basically end of the story. Unless the cache is visible to the OS, the OS simply

The OS can't do anything. The Controller says "Fsync? Sure thing." and that's basically end of the story. Unless the cache is visible to the OS, the OS simply has to accept what the controller says as truth. The issue of a controller lying is to my experience very rare and only really exists for very cheap harddrives, SSDs or SD cards (interesting for RPi). I'm not aware of an enterprise hardware that does this, I suspect if anyone tried they'd be out of business quick.