Seagate hard drive

New hard drive tech will help Seagate crack 5TB barrier in 2014, 20TB in 2020

Seagate on Monday announced that it has sold more than 1 million drives using a new recording technology that will offer consumers 5TB hard drives next year and possibly 20TB drives by 2020.

The technology Seagate is touting—shingled magnetic recording (SMR)—is needed more than ever.

Just as NAND flash is running up against a miniaturization wall, where the circuitry has little room to continue to shrink in size, hard drives face a similar density dilemma. The data tracks on a 1TB hard-drive platter cannot afford to shrink much more, according to Seagate.

The theoretical limit of magnetic storage, called the superparamagnetic limit—about 1Tbit per square inch of storage density—is fast approaching. Increasing the density beyond that will lead to data corruption issues. Currently, Seagate's drives store data at up to 625Gbits per square inch of storage areal density.

SMR is only one of several technology advancements pushing the limits of hard drive capacity. Heat-assisted magnetic recording (HAMR) is expected to take disk drives to 5Tbits per square inch. Seagate rival Western Digital is expected to release helium filled disk drives later this year. The helium provides less resistance than air and so will allow more platters to be stacked closer together.

"With SMR technology, Seagate is on track to improve areal density by up to 25% or 1.25TB per disk, delivering hard drives with the lowest cost per gigabyte and reaching capacities of 5TB and beyond," Mark Re, Seagate's chief technology officer, said in a statement.

Seagate would not disclose which of its drive models today use SMR. It would only say that system makers that use them know they're using them.

Seagate
How tracks are typically spaced using perpendicular magnetic recording.

The principle behind SMR is simple. With the technology, the tracks of a drive basically overlap like the shingles on a roof, thereby allowing Seagate to squeeze more tracks together.

The density problem came about when Seagate and other drive manufacturers pressed the limits of how close they could squeeze tracks together on a drive platter. For a mental picture of platter tracks, think of an LP vinyl record, except on a microscopic level.

The closer the tracks of a drive platter are squeezed together, the more data can fit in a disk drive. But, the closer together the tracks get squeezed, the greater risk of data corruption and read errors—that is, the read/write head of a hard disk drive cannot discern the difference between tracks. In between the tracks are buffer areas to help the read/write heads track accurately.

More platters can be added to a drive, as some drives have today, like a stack of pancakes, but that adds to the height of the drive.

Hard drive density

Hard drives today typically use perpendicular magnetic recording (PMR), a method of laying down data on a platter that creates tracks that are about 75 nanometers wide, which is smaller than a flu virus. Seagate introduced its first PMR drive in 2007. The drive, the Barracuda, held 250GB of data per platter. That grew to 1TB per platter by this year.

While that seems like a lot, Seagate predicts that households currently generating 1TB of data monthly through streaming or creating content, viewing photos, and sharing music will increase that data creation by 20 times over the next two years. So, drive density must grow along with that.

The write portion of a hard drive read/write head—think of a record player needle—is what dictates the width of a track because it needs to be larger to incorporate the technology to record the data. SMR technology overlaps the write portion of tracks, leaving only the read portion exposed for the head to later find.

Seagate
How SMR offers increased density on platters by overlapping tracks

This is how it works: As new data is written, the drive tracks are trimmed, or shingled. Because the reader element on the drive head is smaller than the writer, all data can still be read off the trimmed over overlapped track without compromising data integrity or reliability.

"The HDD industry is experiencing petabyte shipment growth rates greater than 30% per year while at the same time HDD areal density is improving at a rate less than 20% per year," John Rydning, IDC's research vice president, said in a statement. "Shingled magnetic recording technology is a solution that leverages existing drive architecture to help close the gap in these growth rates while at the same time providing a relatively simple yet economical path to higher capacity HDDs for many applications."

One somewhat obvious problem, Seagate admits, is that SMR works best on a new hard drive where tracks are set down sequentially. On older drives, where old tracks are often overwritten, the writes can overlap previously written data on an adjoining track and unintentionally destroy it.

Seagate
How SMR groups tracks into bands

Because of the write overlap issue, SMR groups tracks into bands, where the shingling process stops. This enables an SMR drive to better manage rewrites. Banding also improves the drive's write performance by grouping tracks into bands that optimize the number of tracks that need to be rewritten.

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