Datacenter HDD shipments have been growing at a 45 percent CAGR, roughly doubling the storage capacity of the datacenter every two years. Hyperscale datacenters are also under duress as their storage capacity is more than doubling every year. Unfortunately, areal density increases have slowed to 15 percent per year. Rapid density advancements have slowed to incremental increases as we reach PMR's limit. SMR has experienced limited success in a limited number of use-cases, and HAMR is still five years away from mass production by many estimates.
With no immediate jump in areal density on the horizon, HGST decided to take another path. The HGST Ultrastar He6 innovates by delivering 6TB of capacity through increased head and platter counts in the familiar 3.5-inch form factor. The 7,200 RPM He6 is available in SAS and SATA flavors and features a sustained speed of 177 MB/s and a 64MB cache buffer.
Today's leading HDDs have 5 platters and 10 heads. Simple math deduces that four more heads and two more platters can fit into the 3.5-inch form factor and provide an immediate capacity bump. Simplicity ends there, and air resistance becomes the biggest foe. Adding more platters and heads introduces wind turbulence that creates flutter, vibration, and drag. Extra drag necessitates stronger motors that require more power, and error rates skyrocket due to air buffeting the drive heads.
Helium is one-seventh the density of air and drastically reduces drag and turbulence. The helium concept emerged years ago, but the primary challenge was its penchant for escaping containment. HGST's proprietary HelioSeal technology traps helium and forgoes the use of fasteners, which reduces weight. This leads to a 38 percent lower weight-per-TB that is helpful for restricted floor loading environments. Sealing the drive makes the He6 impervious to outside air, removing restrictive humidity constraints in open-air datacenters. This also makes it well suited for cutting-edge immersion cooling.
Helium's lower wind resistance allows the use of thinner glass-substrate platters, enabling HGST's proprietary 7Stac design that packs 7 platters and 14 heads in the same 1-inch z-height. Less wind resistance also reduces drive motor power consumption. The He6 can significantly reduce cooling costs in large deployments because it runs 4-5 degrees cooler.
The He6 is the only 6TB HDD on the market, and for this evaluation, we compare the HGST Ultrastar He6 to the HGST Ultrastar 7K4000. The 7K4000 currently leads the 7,200 RPM segment in performance, efficiency, and reliability. The 7K4000 comes in 2TB, 3TB, and 4TB capacities, while the He6 is only available at 6TB. The He6 features a small jump in areal density, in tandem with more platters, to provide more capacity. The He6 is also much quieter and 50g lighter, but it takes a step back in performance. Seek time rises to 8.5 ms, and the He6 has a slightly lower sustained transfer rate.
Power consumption is drastically reduced in active and idle states, driving 23 percent lower idle power consumption and 49 percent better Watts-per-TB. Both drives feature a leading 2-million-hour MTBF, a five-year warranty, and the standard 1 per 10^15 BER rate.
The He6 was designed to provide the ultimate in storage density and power efficiency. Its innovative features can be a catalyst for denser storage infrastructure and loosened requirements for open-air datacenters. Let's take a closer look and compare its performance to the leading 7,200 RPM HDD.