Where hard drives are headed


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TrendFocus' Geenen agrees that Serial ATA II drives won't knock high-end SCSI or FC off the top of the stack, but he thinks the effect on the server drive market as a whole could be earthshaking. "If the Serial ATA promise holds," he says, "a lot of companies will choose to walk away either partially or fully from SCSI."

New life for SCSI
Seagate's Macleod disagrees, arguing that Serial ATA "simply does not have the functionality and reliability levels needed for mission-critical class data storage." Macleod acknowledges that Serial ATA could make sense for near-line storage and tape replacement, "but, in general, Serial ATA is a poor choice for truly mission-critical applications."

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Flashing lasers and burning wires
Alternatives to magnetic storage are already on the market, of course: optical drives and solid state disks (SSDs). But no one can seem to figure out how to boost the performance of optical to anywhere near hard drive levels - and although the price of RAM keeps dropping, SSDs remain prohibitively expensive for all but a few high-transaction applications. It remains to be seen whether the whizzy alternatives proposed for the future will have better luck.

Holographic storage is the most frequently mentioned of these. The theory has been around since the 1960s: What if you used two lasers to etch data in a translucent material instead of images? Where the lasers intersect, an interference pattern is created, which can be later read by exposing it to a single beam. The promise of holographic storage is that you could potentially store terabytes in a tiny space. Unfortunately, no one has yet discovered a material displaying the appropriate longevity, speed or photosensitivity characteristics.

Atomic-force microscopy (AFM) stands the best chance of any storage scheme employing a microelectromechanical system (MEMS), which simply refers to a semiconductor integrated with miniscule mechanisms. It actually sounds more primitive than a magnetic drive: First, you heat a microscopic filament so it makes a pit in a plastic disk; later, the filament reads the disk as if it were a teeny phonograph stylus. Recently, IBM demonstrated its AFC technology, code-named Millipede, using a prototype device that stores a terabit per square inch. Though access times are slow, AFM holds the potential to create cheap devices with plastic platters smaller than one inch in diameter - the practical limit for magnetic drives. IBM predicts Millipede could find its way into portable consumer devices as soon as late 2005.
Instead, Macleod believes that the forthcoming Serial-Attached SCSI (SAS) specification - which he sees as a "natural evolution" of current parallel SCSI technology - will have a better chance at succeeding parallel SCSI as the enterprise-class interface of choice. Championed by Compaq, Seagate, IBM, and Maxtor, SAS will exploit some of the development done on Serial ATA, including smaller connectors and a lower command-set overhead. According to the Serial Attached SCSI Working Group, the ultimate goal is to create a universal connector for hard drives, so a single server or storage appliance could accommodate Serial ATA and SAS devices.

The first SAS products are expected to appear in 2004. The new specification will enable 128 devices to be attached to one SCSI bus, a giant step up from the current 16-device limit. And while the fastest current SCSI interface tops out at 320MB/s, top-end SAS devices will sport 600MB/s interfaces by 2005 - twice the top speed proposed for Serial ATA II devices.

Of course, faster interfaces simply raise the ceiling on throughput; it's up to the drive itself to fill that capacity. In fact, today's parallel SCSI drives rarely bump up against the prevalent 160MB/s interface limit. But as Macleod says, "Interface performance is critical in accessing cached data." Over the next few years, he anticipates that Seagate and others will be likely to add larger, smarter buffers to hard drives to increase performance. Already, the incremental performance benefits incurred by the large 8MB buffer in Western Digital's Caviar Special Edition drives have attracted industry attention.

A near future of McDrives?
IBM's Munce notes that new hard drive standards always present multiple opportunities for innovation. For example, future Serial ATA II specs might piggyback support for the development of intelligent drives that understand more about the data they store. We could then see drives that write to disk intelligently - with, say, large media files on the outer tracks for faster transfer rates and small, frequently-accessed files on the inner tracks where everything is packed closer together.

Enterprise drives already use Self Monitoring Analysis and Reporting Technology (SMART) to alert IT to potential problems before they occur. "We see SMART's role expanding to provide our engineers and quality technologists with information to enable ever-more-reliable storage devices," says Macleod.

But added intelligence of this kind, which would require substantial R&D, has no specific time frame. IBM's Almaden research facility is packed with all sorts of great ideas - some of which have made it to market and some which never will. According to Geenen, even miniaturization may take awhile to progress further. "There are a lot of issues that may slow it down, not the least of which is that it will take a significant level of investment and risk-taking to push form-factor downsizing," he says. "And there are very few companies today that are equipped to fund or to take that risk." As Geenen points out, IBM's recent decision to spin off its hard drive operation into a joint venture with Hitachi speaks volumes about the commoditization of mass storage.

True, areal density will continue to increase dramatically. But high-performance server hard drives will be unlikely to exploit those advances, because more bits per square inch means fewer I/Ops per gigabyte - unless high-speed drives get a whole lot smaller in a hurry, which no one anticipates. But that doesn't mean huge-capacity drives will be left out of the data center, says Seagate's Macleod. "For insanely high I/Ops systems, 15K drives are the answer - and in the future, even faster drives or parallel arrays of tiny drives will be the direction. For less I/O-intensive applications like backup storage larger, high-capacity, slower drives provide a much more cost effective answer."

Storage technologists agree that the magnetic hard drive will endure at least until the end of the decade. By that time, new storage schemes - involving lasers or plastic discs - may replace magnetic drives in many applications. Remember, though, rumors of the hard drive's demise have been greatly exaggerated before.

The trend, says Macleod, will be toward drives with ever more application-specific performance and cost characteristics. And for mainstream storage systems, the immediate future appears to lie in cheaper, incrementally faster drives that use redundancy and better monitoring to provide fault tolerance at lower cost. New storage technology just doesn't appear to be right around the corner, astonishing increases in capacity notwithstanding. But cheaper, smaller and slightly faster hardware? You can always count on the computer industry for that.

This was first published in August 2002

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