Small disks, big specs

Hard disk drives have been around for more than 50 years, but the technology is on the cusp of big changes--SAS, a shift to the 2.5-inch form factor and a steady increase in disk drive capacity--that will affect enterprise storage for years to come.

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Disk drives are getting faster, smaller and can hold more data. And the price per GB continues to drop.

The hard disk drive is suddenly hot. The technology, which celebrated its 50th birthday in 2006 and has been the mainstay of enterprise storage for decades, is now on the cusp of big changes that will affect enterprise storage for years to come.

"Two things make hard disk a big deal right now: serial-attached SCSI [SAS] and the shift to the 2.5-inch form factor," says Mike Karp, senior analyst at Enterprise Management Associates (EMA), Boulder, CO. But those are just the most apparent changes that are percolating.

Some of the changes aren't new, like the steady increase in the capacities of hard disk drives (HDDs), which continue to grow by approximately 40% a year. But other developments like the 6Gb/sec speed of the new SAS interface may prove game changing, especially when it migrates from the drive itself to the storage array. Still others like encryption on the disk, the potential to spin disks up and down to conserve energy, long-block (4K) error correction and object-based disk, which promises the ability to use meta data about the stored content, won't have much impact in the short term, but they're swiftly moving out of development labs and into products.

The 2.5-inch server drives have just started to ship, and Dell Inc. is using them in its new PowerVault MD1120, which can house up to 144 drives in 12U of rack space.

The 6Gb/sec SAS drive interfaces are still being certified and, again, it will take time before the arrays come equipped with comparable interfaces. But with demand for storage capacity and performance steadily increasing and pressure to contain energy costs mounting, the latest HDD developments will give storage managers a lot to think about over the next six months to 18 months.

"We're pretty content with what we have for disk right now. If we hit a bottleneck, we'd certainly look at the new things," says Reid Watanabe, program manager at Hawaiian Electric Company Inc. in Honolulu. Watanabe oversees the company's 40TB to 50TB of disk storage and recently added several Hewlett-Packard (HP) Co. Storage Works EVA 8000 arrays. As the HDD enhancements roll out over the coming months, storage managers like Watanabe will begin cherry-picking those that address their issues.

2.5-inch HDDs
Now that 2.5-inch drives offer higher capacities, they appear destined to become the next enterprise storage standard. "You've got a small size, high performance and high capacity," says EMA's Karp. "You can put a lot of these drives in one box and still draw less power." The initial 2.5-inch enterprise drives will spin at 10,000 rpm, but Karp expects 15,000 rpm versions to follow. It's the same story with capacity. The 2.5-inch drives jumped from 146GB to 300GB by mid 2008, but Karp sees them hitting 500GB pretty quickly.

In June, Seagate Technology LLC announced a 2.5-inch enterprise-class drive with impressive specs: 300GB capacity, 10,000 rpm, 60% greater density than 3.5-inch drives, a 6Gb/sec interface, 1.6 million hour mean time between failures (MTBF) and drive-level full-disk encryption.

As the HDD industry struggles to generate low-cost IOPS, 2.5-inch disks combined with faster performance will play a key role. More spindles packed into the array spinning at faster speeds mean more IOPS. And forget about topping out at 15,000 rpm. "With the 2.5-inch drive you can get 20,000 rpm," says Chris Wood, CTO at Sun Microsystems Inc.'s storage and data management practice. As of this writing, no commercial 20,000 rpm drives had been announced.

On top of greater IOPS, the 2.5-inch drives will consume far less energy, even when spinning at 20,000 rpm. "You've got a smaller head and a smaller platter. That gives you a big gain in space and energy," declares Wood. "The industry has reached the tipping point for 2.5-inch drives."

Hawaiian Electric, however, isn't ready to jump at arrays built around 2.5-inch drives for its enterprise storage. "We see 2.5-inch drives for servers," says the firm's Watanabe. For now, the company will stick with the 3.5-inch standard for enterprise storage, at least until the industry standardizes on 2.5-inch drive enterprise arrays.

The Research Foundation of the State University of New York at Albany will pass on 2.5-inch drives, too. "We have a Sun [StorageTek] 9990 SAN and until 2.5-inch disks fit into that we're not interested," says John Busdiecker, director of infrastructure services. As for 6Gb/sec performance: "For us, that's overkill now, although it might be of future interest," he adds.


Energy savings
The new disk drives save energy in several ways:
  • Large 3.5-inch drives (1TB and above) mean fewer spinning disks are required for the same capacity. They also spin at slower speeds.


  • 2.5-inch drives have lighter platters and smaller heads, which require less energy (9W vs. 13W); some laptop drives consume just 1.8W.


  • Future control of spin speed will enable selective slowing or stopping of individual spindles to save more energy.

The future of 3.5-inch
As high-performance, IO-intensive production applications jump to 2.5-inch HDDs, 3.5-inch SATA drives will be increasingly used for archival storage and digital media storage. "We're seeing explosive demand here for Web 2.0, D2D backup and archival," says Sherman Black, senior VP and general manager of Seagate Enterprise Compute Business.

These applications involve rich media, digital media and static data. Backup and archival data is rarely, if ever, accessed. High performance isn't the issue; cheap capacity is. Large capacity, slow SATA drives are ideal.

"1TB drives could do a lot for us, especially for D2D backup," says Kim Mehring, manager at Sandhills Publishing Company's West Data Center in Scottsdale, AZ. Sandhills publishes a number of trade magazines and provides various data services to its clients. "We've already jumped from 500GB to 750GB. 1TB would be even better," says Mehring. Sandhills uses HP's MSA storage for its D2D storage and a dozen HP StorageWorks 600 All-in-One (AiO) Storage System arrays populated with industry-standard 146GB 3.5-inch SAS drives as modular production storage spread between two data centers.

The Research Foundation is interested in 1TB drives, too. It runs the full suite of Oracle Corp. applications and the foundation's Busdiecker says the 1TB drives would be a good fit to archive that application's data.

Seagate began selling a 1.5TB desktop drive last month and enterprise-class 1TB SATA drives are available from several manufacturers. Western Digital Corp. introduced a 7,200 rpm 1TB SATA drive in June. It comes with a 3Gb/sec interface, but sports a 32MB cache to boost performance (retail price $249). In July, Hitachi Global Storage Technologies introduced its Deskstar 7K1000.B 1TB, 3Gb/sec 7,200 rpm 3.5-inch SATA drive, which it claims has "up to 43% idle power [electricity] savings over previous generation products." By 2009, 1TB SATA drives will seem puny when Seagate expects to release a 2TB drive.

"Now you've got dirt cheap, low performance, 1TB 3.5-inch SATA drives. If you combine them with MAID [massive array of idle disk] technology, the HDD industry can challenge tape for archival applications and long-term backup," suggests Sun's Wood.

A sampling of Enterprise Hard Disk Drives

Click here for a sampling of
enterprise hard disk drives (PDF).


Areal density
Areal density refers to how tightly data bits can be packed onto the surface of a spinning platter inside the hard drive and is the key to HDD capacity. Because the size of the platter (2.5 inches or 3.5 inches) is finite, drive makers need to make the bits smaller to increase capacity and pack them more tightly into increasingly narrower tracks that can still be written and read by the magnetic disk drive head.

Storage managers have enjoyed a seemingly endless ride up the areal density curve. As areal density has increased, HDD vendors have been able to reduce the cost per gigabyte of storage to pennies and improve performance. But there's a theoretical limit to this joyride, the superparamagnetic limit, which is the point at which a magnetic bit is so small it can't hold its charge and becomes unstable. The industry appeared to reach this limit a number of times, but at various junctures researchers expanded the amount of data that can be packed on a disk by miraculously pulling another rabbit out of their bag of technical tricks.

The current HDD capacity gains result from the advent of perpendicular storage, by which bits are laid down perpendicular to the surface (vertical) rather than horizontally. "Perpendicular recording technology is good for another three to four more years," says Jim Porter, an industry observer and commentator at Mountain View, CA-based Disk/Trend. Porter has watched the industry overcome the superparamagnetic limit numerous times.

However, it's not clear what the next technical trick will be. The one mentioned most often is multilevel magnetic recording, in which bits are stacked on top of each other and the magnetic heads read and write bits at different depths. "There are probably four things in the hopper. Two may come to pass; it may not be just one thing," says Seagate's Black coyly, reluctant to tip his organization's hand. Others think the solution will entail a change to new materials, such as ceramics.

Fibre Channel (FC) vs. SAS
"Parallel SCSI is at end of life," declares Black. Vendors have begun winding down conventional SCSI products in favor of SAS. The advent of 6Gb/sec SAS, also referred to as SAS 2 or wide SAS, dramatically changes the competitive landscape. At 3Gb/sec, SAS lagged FC's 4Gb/sec performance. "At 6Gb/sec, SAS is going to cannibalize FC market share pretty quickly," says Greg Schulz, founder and senior analyst at StorageIO Group, a research firm in Stillwater, MN.

Hawaiian Electric isn't ready to abandon FC. The organization's Watanabe is comfortable with the performance and reliability of FC for now, but "something like 6Gb/sec SAS might get us to rethink FC," he says. It won't be the only company rethinking the situation. Market research firms Gartner Inc. and IDC see a strong shift from FC to SAS. IDC, for example, predicts that shipments of small form-factor enterprise drives going into enterprise solutions will outnumber 3.5-inch enterprise drive shipments by 2010.


Error protection and encryption
Rounding out the list of upcoming HDD goodies are drive-based encryption and enhanced error protection. Further out is object-based HDD.

"Encryption built into the drive will be a huge thing," predicts Joel Weiss, president at the International Disk Drive Equipment and Materials Association (IDEMA), a Milpitas, CA-based trade association for HDD makers. Ironically, drive-based encryption may be most appealing when the drive reaches end-of-life and gets retired. Vendors report amazement at the amount of data left intact on returned disks. With on-drive encryption that concern goes away; as soon as the drive is separated from the key, the data becomes unreadable. Seagate already offers an enterprise drive with encryption, and it's emerging as a must-have for laptop disk drives (see "Notebook storage," below).


Notebook storage
With newspaper reports of laptops disappearing regularly, disk encryption has emerged as a key feature of notebook drives. The current hard disk drive (HDD) standard for laptops is 2.5-inch SATA with some vendors pushing capacity as high as 500GB.

At one time, a 1-inch HDD was touted for laptops, but no longer. "The 1-inch drive is dead, given up to solid-state disk [SSD]," says Joel Weiss, president at the International Disk Drive Equipment and Materials Association (IDEMA) in Milpitas, CA.

But SSD isn't making much progress either. "Hardly anybody is using SSD [in their notebooks] and those that do are disappointed," says Avi Cohen, managing partner and head of research at Avian Securities LLC, a Boston-based research company. SSD makes minimal impact on battery life, maybe 5% to 7% savings, for a $900 price premium. There are also problems making an SSD's MLC NAND work correctly.

"Wear leveling doesn't make sense on a small amount of SSD. You need at least 200GB, and that's too expensive," adds Cohen. So at least for another year or two the 2.5-inch HDD will continue to reign in the laptop/notebook market.

Encryption can occur at many levels, but not all users feel disk-based encryption is necessary. "We had a conversation about drive-based encryption recently with Sun and decided we'd rather do software encryption," says Busdiecker at The Research Foundation. He feared drive-based encryption might complicate backup.

Sandhills Publishing isn't interested in drive-based encryption either. "At that point, the disk starts getting proprietary. We don't need that level of security," says the firm's Mehring. The company prefers drives to be as interchangeable as possible.

As density increases, error correction becomes increasingly critical. Drives currently use a 512-bit block for error correction. Under development is a 4K block, referred to as a long block. The bigger block will not only enable better error correction, but may free up capacity. "Longer blocks reduce the number of pointers required compared to the small block," explains Schulz, which effectively frees space previously taken by all those pointers. Long-block error correction isn't shipping yet.

Object-based HDD represents an effort to make the disk aware of the content being stored. "It's about tracking meta data at the drive level, almost like an object-based file system," reports Black. Today, object-based disk is a research lab initiative only.

Expect HDD to be around for a long time to come. Tape and solid-state storage have their places, but with continued research and development, HDD will remain the storage mainstay.

This was first published in September 2008

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