special report Storage hardware can't keep indefinitely storing more bits in the same amount of space. When will we run out of disk space, and what will we do when it happens?
In a feature a couple months ago, we discussed how ever-increasing volumes of data are making storage harder to manage, and the various components of a long-term vision that will eventually see storage managed as a service. However, the growth of storage needs has a much more practical and immediate effect on the plumbing layer than it does on the management layer.
The short-term solution to increasing storage capacity is to add more storage boxes. However, with storage volumes doubling every year or two, this solution is hardly going to be popular in space-starved server rooms or with customers of hosting providers who charge by the rack unit. Nor will the accounts department be happy if the cost of buying storage doubles every year. Consequently, vendors of disk, tape, and optical storage devices have roughly kept pace with the growth of storage by increasing storage density -- the amount of stuff that can be stored in the same amount of space -- at approximately the same rate. The per-megabyte price of storage has also been keeping its end of the bargain, halving in about the same time as storage needs and storage capacities double. But there are questions whether this exponential increase in density can continue for much longer before it reaches some fundamental limits. So what are these limits and what technologies will replace tape, disk, and optical when they run out of steam?
Running out of space
"There are some interesting technologies out into the future, but really they're just iterations of technologies we've already got today," says Ian Selway, product manager for network storage solutions at HP. "Until someone makes either atomic or holographic storage a solution, it's just doing more in smaller form factors than we're doing today."
"I've been consistently stunned how much they can get into a standard magnetic disk. There's been talk about moving to other forms for years, but there doesn't seem to be a breakthrough on the horizon, and there doesn't seem to be a problem with increasing the densities [of magnetic disk] for the next five or six years," says Kevin McIsaac, research director at industry analyst the META Group. "And who knows how they'll figure out how to leverage magnetic storage going further. Even tape still has a pretty important useful life because it's very, very low cost."
Even though the storage industry has so far always found ways of increasing the density of data stored on magnetic disks and tapes, it will eventually hit a wall. "One of these days we're going to reach a limit called the superparamagnetic effect, and that's a problem caused by having the bits so close together that I can no longer differentiate between one bit and the adjacent ones," explains Rob Nieboer, storage strategist at StorageTek.
This doesn't mean there's an ominous superparamagnetic effect of Damocles hanging over the storage industry. The semiconductor industry, for example, has overcome some of its "fundamental" limits in recent years and Moore's Law -- the doubling of density every 18 months or so -- has continued unabated. Nieboer remains confident that the storage industry will find ways to sidestep the superparamagnetic effect when it becomes a problem.
"Something on the not-too-distant horizon is called perpendicular recording, where I actually have the bits stand on end perpendicular to the surface of the disk, and I can get a higher areal density that way and pretty good raw data rates. That's probably two to four years out at least," says Nieboer. "That may also lend itself to a thing called 3D recording where you go multiple layers of vertical bits, and you may or may not even have to spin the disk."
Nieboer is more sceptical about the practical value of holographic recording, where bits are recorded in a three-dimensional space. "Holographic storage has been 18 months away for at least the last 10 years that I've been aware of. In fact, it's been in development for more than 20 years and it's never yet become viable," he says.
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