In their recent annoucement HGST touted SMR and their unique helium-filled drives by noting the
World’s First 10TB . . . drive sets unprecedented capacity leadership at the lowest $/TB and watt/TB by harnessing two complementary technologies: HelioSeal technology and Shingled Magnetic Recording (SMR). The additive nature of these two technologies enables the future design platform for HDDs in delivering higher capacity points . . . [and] provides the foundation for all future scaling technologies. . . .
What is shingled magnetic recording?
Disk drives tracks are separated by a small gap to ensure adjacent writes don't corrupt data. In SMR drives, this gap is removed, potentially doubling density, but so far adding 25 to 50 percent.
Write heads lay down a wider track than read heads need. In an SMR disk the write tracks are overlapped, leaving narrow tracks that are fine for the read head. But they can't be overwritten without destroying data on adjacent tracks.
In practice, the tracks on an SMR disk are laid down in groups or bands. The band enables a partial rewrite of the disk. How big that rewrite is depends on the size of the band.
HGST has settled on 256MB bands. That means that to update data, an entire 256MB band must be read, modified and rewritten. If the drive has spare capacity that band could be read, marked available and the modified data could be written elsewhere - handy if you're appending 50MB - similar to what SSDs need to do.
The Storage Bits take
SMR is new and HGST is taking a gamble. But not much of one. Most workloads read much more data than they write, so extra write overhead isn't a big problem.
The workloads with high update levels like transaction processing are moving to SSDs and all flash arrays. Mid-range apps are moving to hybrid arrays that combine hard drives with SSDs.
Traditional storage array sales are tanking as cloud services absorb storage growth. Expect that trend to accelerate as Big Data uptake grows.
Big Data is the market these new drives are winning. The emphasis on cost and energy is the cloud provider's sweet spot.
While the purchase price is higher - thanks to the cost of 7 platters instead of 5 - the helium drives run cooler and use less energy, enabling higher drive packaging density and more reliable operation. I hope HGST brings the benefits of SMR drives to consumers as well.
After all, consumers don't do transaction processing either.
The storage business continues to find new niches. HGST will succeed with the new helium/SMR drives.
Comments welcome, of course.