Flash and persistent memory technologies like Intel Optane are where you look for storage speed, but hard drives continue to be the answer for nearline storage density. And while Seagate and Western Digital’s upcoming 16TB hard drives will need novel next-generation energy assisted magnetic recording technologies to get to that capacity, Toshiba is going the tried-and-true route. Its recently announced helium-sealed 16TB MGO8-series HDD uses magnetic recording technology, switching to Two-Dimensional Magnetic Recording, or TDMR.

The nine-platter 3.5” MG08 is a drop-in replacement for existing drives and offers very standard specifications – but with more storage capacity. It’s a 7200rpm drive, with 512MB cache buffer, 6Gbit/s SATA or 12Gbit/s SAS interfaces, industry standard 2.5 million-hour Mean Time Between Failures (MTTF), and 550TB/year workload rating for 24/7 operation.

The combination of helium and a 2D read head improve density and reduce power costs for scale-out cloud storage. As 16TB becomes the standard for cloud, it will leave more 14TB drives available for enterprise customers. But achieving still higher capacities in future drives will mean moving to newer technologies using microwaves or lasers to increase area densities, or even vacuum-sealed drives with no air at all. The good news is those technologies could also drop prices on lower-capacity drives, benefitting more customers.

Seagate introduced the first helium-sealed hard drives in 2013, while Toshiba’s new product is only its second helium model; it has the same laser-welded mechanical enclosure with nine platters as the previous, 14TB, model, with the extra capacity coming from increased areal density thanks to the move to TDMR.

“Adding a second reader element in the head allows us to weed out some of the stray signal interference form adjacent recording tracks and achieve a better signal-to-noise ratio when doing read operations,” Scott Wright, director of HDD product marketing for Toshiba America Electronic Components, told Data Center Knowledge in an interview.

“That allows us to achieve a higher track pitch; we put the tracks a little closer together. We’ve also made improvements to the writer design to modestly improve the write performance of the head elements on the ends of the arms that glide over the medium at nanometer fly heights.”

Areal Dynamics

As with Toshiba’s other high-capacity drives, there’s a persistent write cache in case of power loss while the drive is aligning the write to the physical sectors. That makes it a good way to add high capacity to legacy systems when the 4K sector drive is emulating 512 byte sectors. That will appeal to enterprise buyers, but they’re more likely to pick up last year’s 14TB models; the 16TB drives by Toshiba, Seagate, or Western Digital hitting the market this year will get snapped up by hyperscale cloud platforms.

Higher density and greater Watt-per-terabyte power efficiency of helium-sealed drives makes cloud providers, and hybrid cloud and scale-out storage vendors the main market for these 16GB drives, Wright said. “You're saving 3.5W to 4W of power versus a conventional design, and when you're deploying 100,000 drives, saving that much power is a very big operational cost saving.

“If I need to deploy a petabyte of storage, think about how many devices, how many racks, how much less equipment, how many fewer slots do I need to deploy a petabyte if I'm using 16GB rather than 14TB or 12TB or 10TB. You need fewer slots in the infrastructure and potentially fewer racks to deploy a target storage capacity.”

Buyers may not care that much about the technology inside the drive, Steve McDowell, senior analyst for storage and converged systems at Moor Insights & Strategy, told us, but they do care about being able to have more capacity in the same rack space.

The first MG08 units will be sampling to customers at the end of January, with vendors qualifying the 16TB drive in the first half of 2019, followed by ramping volumes in the second half of the year.

Although Toshiba isn’t yet talking specific pricing beyond “pennies per gigabyte,” Wright predicted that the 16TB model will be price-competitive with current 14TB units, taking into account the price premium of helium-sealed designs over air-filled drives, which are easier to manufacture.

Denser and Cheaper

Even higher capacity hard drives in the future will likely require more than incremental improvements such as a second reader element. Increasing areal density means individual bit sizes on the player get smaller. At a smaller bit size, the energy it takes to change a bit from 0 to 1 goes down, and at a certain point, the ambient temperature inside the hard drive could be enough to do it. Higher-density platters need to use material that’s harder to magnetize. But as write heads get smaller, to fit more tracks on the platter, they aren’t strong enough to magnetize bits on these higher coercivity platters.

The simplest approach is Singled Magnetic Recording, which overlaps the magnetic recording tracks (like shingles on a roof) instead of using parallel tracks, using larger writer heads that can magnetize the bits on the denser platter. SMR could increase the 16TB capacity of the MG08 to over 17TB, but overlapping writes mean previous writes can be erased and have to be rewritten, leading to potentially slower write speeds.

Heat-Assisted Magnetic Recording, or HAMR, uses a laser diode to heat the drive platter to make it easier to write the bit. That’s the approach Seagate is using in its 16TB drive. Western Digital chose Microwave-Assisted Magnetic Recording for its 16TB hard drives, and Toshiba will use that for future generations of its hard drives. “MAMR uses microwave energy and sophisticated spin torque physics to impart energy to the media to enable the bits to flip,” Wright explained. A spin torque oscillator on the write head will produce 20-40GHz microwaves that lower the resistance of the bit, so it doesn’t need as much power to write it; that could deliver capacities up to 40TB, although they’re likely to start at 18TB.

MAMR is more of an evolution in hard drive heads and media than HAMR. “We can leverage a lot of the current methodologies because we’re not adding components like laser diodes; it just needs a different wafer design to produce the microwave capability,” Wright said. “We’re pretty confident MAMR can deliver the same sort of specifications and reliability like MTBF that we have with shipping products today. We don't anticipate any big swing in device power requirements from implementing MAMR.”

Innovation and Choice

HAMR will require more scrutiny, McDowell suggested, and that makes Toshiba’s new 16GB drives appealing.

“What I like about Toshiba’s approach, versus Seagate’s HAMR, is that it’s based on long-proven technology,” he said. “The new HAMR drives need time in the field to really understand the reliability and operating characteristics. There’s an early-adopter risk for HAMR that doesn’t exist with helium-filled drives.”

And when Toshiba does adopt MAMR, it will also use it for 4TB-12TB drives, Wright said. “That’s the sweet spot in the nearline hard drive market, and we can apply MAMR technology to help reduce costs and improve performance of those capacities.”

Whichever energy-assisted recording system wins, hard drive capacity is going to continue improving. As Wright suggested, that would keep hard drives competitive. “I don’t see us hitting the wall any time soon. Helium has helped to change the calculus and the specs about reliability, and the net result is that hard drives are going to continue to be deployed as the storage technology of choice for low-cost capacity across the spectrum of use cases.”

This year will see a fight over nearline storage formats, McDowell predicted. “QLC NAND products are starting to ship, and the long-term economics of QLC SSDs versus HDDs for high-capacity, high-density storage seems to favor QLC. You get vastly increased storage densities without the power and cooling required by vast rack units full of spinning disks.”

The upfront cost of QLC NAND might be off-putting of course, but he welcomed the wide range of choices. “There is a tremendous amount of innovation happening in the storage world right now, and that only serves to benefit IT buyers and practitioners.”