D2D2T = Disk to Disk to Tape;
D2D2H = Disk to Disk to Holographic Storage.
InPhase finally commercialized the holographic storage. From the news floating in Web, we know first product has 300GB per media, around 27MB/s write speed. The media is about $180 each and the drive is over $10K.
So this is why I think we need D2D2H:
- You need about 3 hours ((300GB / 27MB/s)) to write a full medium, this speed is too slow for nearline storage. So you need a disk-based staging area as a faster persistent cache;
- Normal backup/archive does not need 300GB capacity thus you need many day’s backup in order to fill one medium. You do not want to take the medium in and out of the drive everyday right? So you still need a disk-based staging area to pile up these data;
- You can not write to multiple media via _one_ drive at same time. And you do want to share this expensive drive among multiple peers. So you need a disk-based staging area to support multiple streams.
- What else?…

Virtual ROM support « BlackMagic said
[...] Seriously, this can be used as WORM archiving purpose. Or do a disk staging for D2D2H. [...]