I've heard rumors of disks that claim to support cache flushes but 
really just ignore them, but have never heard any specifics of model 
numbers, etc. which are known to do this, so it may just be legend. If 
we do have such knowledge then we should really be blacklisting those 
drives and warning the user that we can't ensure data integrity. (Even 
powering down the system would be unsafe in this case.)

This should not be the case for any vaguely modern drive. The standard
requires the drive flushes the cache if sent the command and the size of
caches on modern drives rather require it.

Alan