The humble hard drive doesn’t get much respect these days. Once SSDs started hitting the consumer market, it quickly became clear there was no way hard drive performance would compete in the long term. Hard drive capacities have continued to grow, thanks to new recording technologies and the use of helium inside the drives themselves, but performance improvements have been minimal. Seagate plans to change that in the near future, with new technology that could double hard drive performance.
There are several ways to improve hard drive performance. Fifteen years ago, Western Digital launched various 7200 RPM drives with a larger cache (8MB compared with 2MB on an 80GB drive). All HDDs today use memory caches, even if the ratio of cache size to disk size has fallen sharply.
The next way to increase HDD performance is to increase the rate at which the drive spins. A drive spinning at 15,000 RPM will obviously outperform a drive spinning at 7200 RPM, assuming identical firmware and workloads. But spinning a drive faster comes with its own set of problems: Such drives are obviously louder, it’s harder to build components that can withstand the higher spin rate, and 10K or 15K drives draw more power than their 7200 RPM cousins.
The third way, and the method Seagate has chosen, is to design a drive with multiple actuators. The idea of using multiple actuators isn’t new, and Seagate has experimented with it in the past, but had deemed the approach ineffective due to design challenges, higher drive weights, and additional material costs.
Standard hard drives have one actuator arm, as shown below:
Seagate’s largest actuator arm has 8 platters and 16 heads — but the heads are all mounted to a single structure. Data tracks on the platters are too small to allow all of the heads to align simultaneously, sharply limiting read/write throughput, particularly in random workloads. Seagate’s new design doubles the number of actuators and halves the number of heads. Instead of one actuator with 16 heads, there are now two actuators with 16 heads, each capable of operating independently from the other. The drive can run two different read or write operations at once, provided each is handled by a dedicated actuator. It can also perform two commands in parallel and write from one head while reading from the other.
In its first generation, Seagate’s Multi Actuator technology will equip hard drives with dual actuators (two actuators). With two actuators operating on a single pivot point, each actuator will control half of the drive’s arms. Half the drive’s recording heads will operate together as a unit, while the other half will operate independently as a separate unit. This enables a hard drive to double its performance while maintaining the same capacity as that of a single actuator drive.
Why Bother Boosting Performance?
It might seem silly to worry about boosting hard drive performance when the gap between HDDs and SSDs is so large, but Seagate isn’t claiming this new technology will put SSDs and HDDs at parity. The reason overall drive performance needs to increase is because rising drive capacities are useless if you can’t write data to them in a reasonable amount of time.
Consider this: Even if you could maintain a constant 250MB/s write speed to a 20TB hard drive, it would take you 24 hours to fill the drive under perfect conditions. Since conditions aren’t perfect and write speeds slow down as you reach the outer edge of the platter, it would actually take longer. Enterprise organizations that would otherwise be interested in the high capacity drives Seagate brings to market might understandably balk at deploying RAID arrays that take 1-2 days to recover from a drive failure.
According to Seagate, the drives will offer multiple access streams that users can tap for various types of workloads or tasks. Long-term, Seagate wants to expand up to four simultaneous actuators, potentially doubling transfer rates again.
Now read: How do SSDs work?
Published at Thu, 21 Dec 2017 14:27:57 +0000