Western Digital unveils 20TB OptiNAND hard drive, pledges 50TB to follow

New flash-and-platter architecture offers 'breakthrough in storage that works differently,' firm claims


Western Digital has announced a "breakthrough in storage that works differently," in the form of a new architecture combining traditional platters with solid-state flash: OptiNAND.

Adding flash to traditional mechanical hard drives is not a new concept. Western Digital announced its first work on the concept back in 2011 after being beaten to market by rival Seagate's Momentus XT, a year prior. In both cases, the solid-state flash acted as a temporary buffer for the most commonly accessed data - attempting to blend the best of both storage worlds.

OptiNAND, though, is positioned differently. Rather than simply improving throughput and access time for the user's most commonly examined data, an OptiNAND-enabled drive is claimed to offer increased overall capacity, improved performance across the whole disk, and a fiftyfold increase in the amount of data retained if you accidentally pull the power in the middle of a write.

The heart of the system, beyond the spinning platters themselves, is a Universal Flash Storage (UFS)-standard Embedded Flash Drive (EFD) dubbed iNAND, developed at Western Digital subsidiary SanDisk. Rather than acting as a simple cache, the iNAND disk handles metadata on write positions and volumes - as part of a refresh system meant to avoid adjacent track interference, where a frequently written track will begin to influence data stored on the tracks around it.

"It used to be, not that many generations ago, that you could write 10,000 times before needing to refresh sectors on either side," Western Digital engineering fellow David Hall explained in an interview for the company blog. "And then as we pushed the tracks closer and closer together, it went to 100, then 50, then 10, and now for some sectors, it's as low as six."

Traditional refresh systems rely on tracking these metadata in DRAM, but the accuracy is limited. Tracking the same metadata in more capacious iNAND, or so Western Digital has claimed, improves the accuracy - and allows its engineers to boost the areal density of the mechanical portions of the drive, packing more storage into the same number of platters.

The first OptiNAND drives, sampling to "select customers" now, combine the technology with energy-assisted perpendicular magnetic recording (ePMR) to offer 20TB of storage across nine platters - 2.2TB per platter, the company's highest areal density yet.

At the same time OptiNAND is claimed to offer boosted performance by reducing the number of track interference refreshes required as well as the number of write-cache flushes. The latter also ties in to claims of improved reliability, with WD having claimed that an OptiNAND drive can retain "nearly 50x more customer data" in the event of an unexpected shutdown.

"With our IP and world-class development teams in HDD and flash, we are able to continuously push the boundaries of innovation to improve our customers' storage infrastructure," boasted Siva Sivaram, president of global technology and strategy at Western Digital.

"We have had an extraordinary journey of HDD innovation. We changed everything with HelioSeal in 2013; were first to ship energy-assisted HDDs in volume in 2019; and now we’re going to lead again with OptiNAND technology. This architecture will underpin our HDD technology roadmap for multiple generations as we expect that an ePMR HDD with OptiNAND will reach 50TB in the second half of the decade."

Western Digital had not responded to a query regarding pricing and commercial availability of the 20TB OptiNAND drive at the time of publication. ®

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