HVD is essentially dead.  It was an expensive concept in 2004 and both HDD and SSD have gotten significantly cheaper since then.  Lots of hype, lots of promises, lots of missed deadlines.  Silicon is an amazing thing.  A 1024 GB flash drive is essentially a 512 GB flash drive with chips that have double the density.  If you can make one you can eventually make the other.   Moore's law eventually means the larger one is cheaper than the smaller one use to be.  Look at memory (64K to 16GB) or CPU speed (1 Mhz to 8 cores @ 3.5 GHz) over 40 years.  Optical has never been able to match that kind of progress.