Western Digital has introduced the industry’s first 20TB hard drives with an integrated iNAND UFS Embedded Flash Drive (EFD) to improve performance, reliability and capacity. The company’s OptiNAND architecture does not use 3D NAND memory for caching, but instead uses it to store various metadata to improve the key properties of hard drives.
The 20 TB HDDs from Western Digital with OptiNAND technology are based on nine 2.2 TB ePMR disks (Energy-Assisted Vertical Magnetic Recording Technology), a three-stage actuator technology for more precise positioning of the read / write heads, an iNAND -UFS drive of unknown capacity, the 3D uses TLC NAND storage and the company’s custom system-on-chip (SoC) that controls the drive and the communication between the HDD and EFD.
Modern hard drives store gigabytes of metadata on rotating media because they cannot be stored inexpensively in local DRAM and serial NAND. HDDs store repeatable runout (RRO) metadata (the portion of the position error signal that is repeatable for each spindle revolution) and write operation metadata at the track level to account for increased adjacent track interference (ATI). With OptiNAND, RRO and writes are stored on the iNAND drive, which frees up space on the rotating media, the metadata is available faster and the number of metadata-related reads / writes is reduced, which further improves the performance (ex . random read / write performance). In addition, the EFD stores writes at the sector level, which optimizes memory requirements and reduces the number of ATI updates to improve performance.
As the surface density of modern HDDs increases, so does the amount of metadata that have to be stored on the drive. Also, things like ATI affect the performance of ePMR-based HDDs more than they did before (something that can be solved with HAMR or MAMR magnetic recording technologies, which greatly improve signal quality, or TDMR read heads, which can read data more reliably). So it makes a lot of sense to move metadata off rotating media and put it on a flash-based drive.
In addition, the iNAND EFD can be used to store over 100MB of write cache data in the event of an Emergency Stop Event (EPO), improving the reliability of an OptiNAND-enhanced HDD. Typically, Western Digital drives only store about 2MB of write cache data on serial flash. In addition, HDDs with OptiNAND can reduce their latency with an integrated iNAND EFD and corresponding firmware optimizations.
From a host perspective, the HDDs from Western Digital based on the OptiNAND architecture should work just like other drives without NAND flash. To this end, at least some of the company’s customers will be able to fit the new drives into existing machines, provided their 3.5-inch bays can handle the slightly higher power consumption of iNAND-enhanced HDDs. Given that Western Digital’s exascale customers tend to qualify their drives prior to deployment, expect the drives to be shipped in bulk for a few months (or even quarters).
Western Digital says its OptiNAND technology will be used in several generations of its upcoming HDDs, including those based on ePMR and its successors.
“With our IP and world-class HDD and Flash development teams, we are able to continually push the boundaries of innovation to improve our customers’ storage infrastructure,” said Siva Sivaram, president of global technology and strategy, Western Digital. “We have had an extraordinary journey in HDD innovation. We changed everything with HelioSeal in 2013, we were the first to ship energy-assisted HDDs in large numbers in 2019, and now we will be leading again with OptiNAND technology. This architecture will be our HDD technology roadmap for several generations as we expect an ePMR HDD with OptiNAND to reach 50TB in the second half of the decade. “
The manufacturer doesn’t say how much adding an iNAND EFD will affect the cost of their HDDs, but it is obvious that their bill of materials will increase with an additional component and a powerful SoC controller. Given that Western Digital’s OptiNAND architecture has a number of advantages over traditional HDD architectures, it is likely that the manufacturer will charge an additional charge for these drives.