Comment 1 for bug 1437367

The documentation of FlushFileBuffers() only mentions that consoles cannot be flushed. It doesn't specifically mention physical drives, but it does explicitly mention that whole volumes can be flushed this way:

https://msdn.microsoft.com/en-us/library/windows/desktop/aa364439%28v=vs.85%29.aspx

Of course, I'm not really a Windows expert, so my reading of this may be wrong. If anyone knows how physical drives are supposed to be flushed other than with FlushFileBuffers(), we can certainly implement that in qemu.

In any case, just disabling the flush is not advisable as it may harm data integrity in case of crashes/power failure. If you really want to disable it, the cache=unsafe option should avoid the calls.