Seagate has finally unveiled the specifications on its upcoming dual actuator hard drives. The Mach.2 drive family will be introduced with the Mach.2 Exos 2X14. The hard drive offers 14TB of capacity in “two independently addressable 7TB logical units.”
The 3.5-inch 12Gb/s SAS drive is capable of a maximum sequential transfer rate of 524MB/s, which is substantially faster than any other hard drive on the market. While the 7200 RPM spindle speed isn’t particularly fast compared with the 10K and 15K drives that exist already, Seagate’s dual actuator technology outperforms them all.
Seagate’s Exos 15E900 is a 2.5-inch 900GB HDD with lower claimed latency (2ms compared with 4ms) but a sequential transfer rate of 210-300MB/s. The company’s higher capacity enterprise Exos HDDs claim up to 270MB/s in sequential transfer rates. The 524MB/s for the Exos 2X14 is high enough to match or exceed the performance of early SATA SSDs, though these, of course, are scarcely the competition.
Seagate actually goes into some detail on why it brought dual actuator drives to market. Hard drives have typically gotten faster in three ways: Increased spindle speeds, the integration of drive cache, and command queueing. Hard drives hit 7200 RPM with Seagate’s Barracuda 1 in 1992, drive caches were popularized by drives like the WD800JB in 2002, and Seagate introduced Native Command Queueing (NCQ) support for HDD’s in 2004. Now, in 2021, we’ve got dual actuator drives.
There’s a fourth way to improve HDD performance worth mentioning, though it isn’t really related to any technological advances. Short stroking a drive stores data only on the outer edges of the platter, reducing seek times and improving transfer rates. There is no reason why the Seagate Exos 2X14 couldn’t be short-stroked as well to maintain a higher level of performance, though we don’t know how large the gain would be. Seagate is marketing this drive as a solution to short stroking, so you aren’t going to see them talking about the 2X14 in that configuration.
The reason we needed dual actuators now, according to Seagate, is that HDD performance per terabyte isn’t keeping up with the needs of today’s enterprise customers. Spindle speeds in excess of 15,000 RPM aren’t practical, and the vibrations created by multiple drives running at this speed in an enclosure can harm their performance. Hard drives, if you were not aware, hate being screamed at.
According to Seagate, the number of IOPS/TB offered by conventional hard drives has been dropping for years. If your application requires a minimum IOPS/TB ratio of 7.0, you can’t use an HDD of more than 12TB while retaining that performance metric. If you buy 20TB drives, the extra capacity will not be used, in order to retain the necessary I/O performance.
The boosted performance available from dual actuator drives solves this problem, creating the green line at the top. This allows a 24TB HDD to offer a virtually identical IOPS/TB ratio to a 12TB drive with just one actuator.
SAS 12Gb/s was used over SATA for several reasons. The first-generation Mach.2 drive is expected to nearly saturate the SATA bus, which makes SAS 12Gb/s a better option for the long term. The two actuators are fully independent and Seagate claims the measured, real-world performance improvement of a dual actuator is consistently in the 1.85x – 2x range. Mach.2 drives can even be RAIDed internally, though Seagate cautions against relying on one drive for redundancy, given that dual actuators don’t mean the entire physical drive is duplicated/protected.
Dual actuators aren’t going to give HDDs the performance or responsiveness of SSDs, because no magnetic spinning disc can ever match the performance of a solid-state drive. Hard drives remain important to the data center market; Microsoft and Seagate partnered on these drives specifically to boost performance in a single drive bay. Hard drives are increasingly rare in consumer products, but enterprise and business shipments have been less affected. Enterprise drive sales rose 1.9 percent in 2020, compared with an 18.2 percent decline for the entire HDD market. Moving to dual actuators is one way for Seagate to emphasize performance in the markets where spinning disks continue to matter the most.
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