Apple's custom NVMes are amazingly fast – if you don't care about data integrity
Think about what's going on in the controller running any page access SSD.You have wear leveling trying to keep things from blowing holes in certain physical pages.  In certain cell architectures you can only write to pages that have previously been erased. Once you do write the data to the silicon... it's not really written anyway, because the tables and data structures that map that to the virtual table the host sees on boot also have to be written.It is entirely reasonable that a system that does 100k honest sustained write I/O per second would come to its knees if you're insistent enough to actually want a full, real, power cycle proof, sync.To do an actual full sync, where it could come back from power off... requires flushing all of those layers.  Nothing is optimized to do that. I'm amazed that it can happen 40 times per second.It's possible that you could speed this up a bit, but somewhere there's an actual non-wear leveled single page of data that tells the drive how to remap things to be useful... I strongly suspect writing that page frequently would eat the drive life up in somewhere between 0.1 and 20 million cycles. After that point, the drive would be toast.I agree with the other thread that actually flushing is likely to be a very, very well guarded bit of info.