Optical Data Storage Could Light VOD

For cable operators knitting together video-on-demand systems these days, speed and capacity are front-and-center issues — particularly now that HDTV content is starting to enter the mix.

But while server vendors are seeing upgrades to the tried-and-true magnetic disk storage now humming in VOD systems, there may be another technology on the horizon that could one day shed better light on capacity and stream speed: Holographic data storage.

It sounds more like Star Trek
than cable tech, but holographic data storage research has been around for more than 20 years.

Compared to traditional hard drives — which coil data into tracks around the surface of a spinning magnetic disk — holographic data storage records two-dimensional "pages" of information within an optical storage material such as a crystal or a polymer disk.

The data can then be retrieved by shining a laser back through the material.

By changing the angle of the laser beam and the wavelength of the laser light, multiple pages of data can be stored throughout the entire storage material — not just on the surface, as with DVDs or magnetic disk systems.

Futuristic as they may be, holographic techniques do promise comparable or much-greater storage capacity, durability and faster data-retrieval rates that could be useful in VOD systems.

So while VOD-systems providers such as nCUBE Corp. are not actively developing holographic data systems, they are watching that technology.

"In terms of actually applying it directly to the systems we are deploying now — no, it is too far out for us to really say, 'Hey, there is a definite point at which we could see doing this,' " said Joe Matarese, nCUBE's chief technology officer. "But yes, this is something we are aware of, and something that is interesting."

On the storage side, holographic data development is focusing on two types — one is a polymer disk, while the other trades on solid crystals of iron-laced lithium niobate.

While the first-generation technologies are offering comparable storage capacity compared to many magnetic disk-based products, the crystal storage could potentially store a whopping 1 Terabyte — or 1 million megabytes — of information in a volume the size of a sugar cube.

One small company in the thick of the holographic storage hunt is InPhase Technologies, a Longmont, Colo., spin-off of Bell Laboratories.

InPhase's first generation product expected in 2005 will be a "write-once" storage system offering about 200 Gigabytes capacity on a 5.25-inch disk.

Rapid retrieval

That's roughly comparable to high-end magnetic video server disks, which top out at about 146 Megabytes on a 3.5-inch disk.

But it's in the data retrieval rate that the early holographic products will have the greatest advantage, according to Bill Wilson, InPhase's chief scientist.

"Because the information is stored not in a bit-wise fashion but a page-wise fashion, you have the potential for very, very high data rates," Wilson said. "Even in first-generation products you are going to see data rates that are going to be 20 to 50 Megabits per second for read and write."

InPhase is targeting its Tapestry data storage systems for video archiving among news and media services. While it isn't a focus for InPhase right now, VOD systems could see an application as a VOD central archive.

"Because it is random access, and because it is relatively high-speed, you can actually get information off of it fairly quickly," Wilson said. "If it takes me 20 minutes to search a tape to find Camille, I probably won't offer that as a title. But if I can go and find it in three or four seconds, it gives me a lot more flexibility in what I could offer in a video server."

It could also offer savings in maintenance costs over time compared to older storage technologies.

"In a holographic system, the media is going to have 50-year archival life, and it won't require any special handling," Wilson said. "In that sense, the real cost benefit if you have a large archive is that the total cost of operating that drive drops pretty dramatically."

While holographic data storage might hold promise for future video-server systems, there are more than a few hurdles blocking its path.

Start-ups like InPhase have come up with suitable polymer disk materials, but the hunt for the much higher-capacity crystal storage material has yet to produce a worthy candidate that works and can be cheaply produced.

Just as Thomas Edison had to go through hundreds of materials for light-bulb filaments before hitting on tungsten, so too must these researchers find just the right material to support holographic data storage.

"The guys that are doing the holographic research tend to know what kinds of materials to look at," said Branko Gerovac, vice president of research at SeaChange International Inc. "So they are not gambling as much as Thomas Edison did, but whether they are going to come up with something is not assured."

And improvements to good old-fashioned magnetic disk storage are driving down hardware prices while driving up capacity.

"With the research technologies, it looks like there is another factor of four to eight that can be achieved," Gerovac said. "Magnetic disks are not going away any time soon, although it is getting significantly harder to produce them."

HD content will increase the demands for storage and retrieval of content on VOD systems in the coming years. But the volume of films, TV shows and other content offered on most systems isn't as yet coming close to the maximum capacity of most conventional systems.

"We are actually able to do quite well in terms of the cost of the system with the existing disk drive technology," Matarese said. "Given we can construct a server that delivers a price per stream that scales up to a system that has 170,000 hours worth of content — and that is far beyond what people are doing immediately, but definitely where they are headed.

"Whatever does come along next and whatever impresses us as a very interesting next step to pursue, it really does have to be at this point a much, much less expensive technology to deploy."

Fellow VOD provider Concurrent Computer Corp. is even more skeptical, based on feedback from its own MSO customers.

'A bit out there'

Instead, it has introduced a system that separates the processing for logging in, storing and streaming out VOD titles, thereby allowing operators to add modules as their service grows while maintaining speedy performance.

Holographic data storage "is probably is a bit out there for mainstream systems," said Bruce Bradley, Concurrent's vice president of product management. "As VOD is maturing, we get more and more documented feedback from our MSOs, and one in particular gives us some very strong wording that they do not want very futuristic technology. They want proven technologies. This is now a mainstream business for them. They want to get out of the experimentation phase."

But others think that given the progression of video server technology, holographic storage may one day turn the economic corner to find its way into cable systems.

"When we build a video server, we build a computer that is optimized to streaming video," Gerovac said. "So any computer technology is game for that process. So holographic storage becomes available as a computer technology, then it will simply be a matter of time before it is cost-effective for video server and video-on-demand technology."