Western Digital to Demo Dual Actuator HDD, Will Use SMR to Hit 18TB Capacity

Western Digital to Demo Dual Actuator HDD, Will Use SMR to Hit 18TB Capacity

Hard drive manufacturers are still looking for ways to improve device performance and capacity, even in the modern age of solid-state storage. Earlier this year, during CES, we discussed how Seagate was using dual actuators to improve its hard drive performance. Now, Western Digital is planning its own dual actuator drive and will show off a prototype next week at the Open Compute Project summit.

Western Digital to Demo Dual Actuator HDD, Will Use SMR to Hit 18TB Capacity

The use of dual actuators is important to keep the number of IOPS/TB steady as the total capacity of the drive increases. Dual actuators should provide a roughly 2x increase in performance, including sequential read/write speeds of up to ~500MB/s. Doubling actuators increases power consumption, but not to the same degree as actually doubling up on all drive components; Western Digital expects a dual actuator drive to consume ~26 percent less energy than a pair of hard drives would in the same instance.

WD Won’t Use MAMR for Initial 18TB Drives

We’ve discussed before how Seagate and Western Digital are pursuing two different types of technology to bring higher-capacity hard drives to market: HAMR and MAMR. Both technologies accomplish the same goal — they increase the coercivity of the magnetic medium, making it easier to write data to the drive. Both companies have pooh-poohed the technological efforts of the other, but there’s a not-so-subtle difference between them. Seagate has committed entirely to HAMR (Heat-Assisted Magnetic Recording), while WD is working on both HAMR and MAMR (Microwave-Assisted Magnetic Recording), the latter of which it intends to bring to market first. There have been questions raised about whether or not MAMR would scale as well as HAMR, and there may be small signs of trouble afoot.

Click to enlarge
Click to enlarge

Originally, Western Digital announced that it would launch 16TB and 18TB drives using both MAMR and CMR (Conventional Magnetic Recording) as opposed to SMR (Shingled Magnetic Recording). CMR lays down data in broad stripes. Shingled magnetic recording packs the data tracks more tightly, overlapping them one atop the other. The problem with SMR is that when you write data to one track, you also rewrite data on adjacent tracks. This means that while an SMR drive’s sequential performance is typically fine, random write performance suffers as the drive has to rewrite multiple tracks of data at once. SMR is a technology developed to increase density at the cost of performance.

The shift to HAMR / MAMR was supposed to make such technologies unnecessary. But, as Computerbase.de reports, Western Digital has subtly updated its guidance. In January, the company said it would launch an 18TB HDD with CMR. Now, it’s saying the same drive will use SMR. The first version of the slide above, published in January, identified the 18TB drive as a CMR model. The new guidance says SMR.

This could be a typo or a sign that WD has changed its plans, but either way, it suggests that MAMR might be having some scaling issues. Seagate apparently plans to return to CMR for future products, even as capacities rise. SMR may be useful for boosting capacities, but it doesn’t really offer any features that would make companies want to deploy it in the field if CMR is available.

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