Western Digital Corp. (WD) is combining NAND and spinning disk, but don’t call it a hybrid drive.

Rather, the company’s OptiNAND is a new drive architecture that uses NAND flash to enhance the traditional hard disk drive (HDD) by embedding it with an iNAND embedded flash drive (EFD). WD president of global technology and strategy Siva Sivaram said OptiNAND is the result of combining the company’s expertise in flash storage and spinning disk, including a legacy of hard drive architecture innovations through its HGST acquisition.

He said what makes OptiNAND different from a hybrid drive is that the flash isn’t used to store user data.

“Flash is really intended to enhance the drive capabilities. This is not being inserted in the drive in the data flow.” Instead, the vertically integrated iNAND combined with an enhanced firmware algorithm and system-on-a-chip (SoC) innovations improves the capacity, performance, and reliability of the HDD. WD’s new OptiNAND-enabled memory hierarchy uses the drive SoC to control communication with the iNAND EFD using the Universal Flash Storage (UFS), which is commonly used in mobile devices and automotive applications.

Sivaram said this allows key drive housekeeping functions to take advantage of an increase in metadata capability. The embedded flash has its own controller and proprietary firmware because the flash also needs to be managed.

A key benefit of the OptiNAND architecture is that when combined with triple stage actuator (TSA) technology, it enables higher areal density through increased tracks per inch (TPI). This is accomplished by using gigabytes of metadata generated by the HDD that was too large to be cost-effectively maintained in DRAM. The iNAND EFD takes over the role to store and access this in real time and frees up space on the rotating media for user data. Sivaram said the greater number of tracks per inch, the higher the amount of storage on the disk. “It allows for capacity growth without the addition of an extra disk or heads.”

HDDs normally record write operations at the track level and refreshes were done for entire tracks, but OptiNAND records write operations in iNAND at the sector level. This metadata is used to refresh sectors instead of whole tracks. By eliminating excess refreshes, said Sivaram, tracks can be placed closer together without performance loss because there’s no interruption to the data flow on the drive while background operations are taking place. He said the presence of the iNAND EFD also allows for features to be developed later on and any necessary hooks to be placed in the drive.

Ashley Gorakhpurwalla, general manager of WD’s HDD business, doesn’t see any limits for OptiNAND capacity-wise, but the first generation that’s sampling with customers delivers as much as 20TB in a nine-disk platform with 2.2TB per platter. “We’re well into the ramp of volume production and consumption by our customers.” Improvements in drive latency are achieved by proprietary optimizations to drive firmware focused on requiring fewer adjacent track interference (ATI) refreshes and reducing the need for write cache flushes in write cache-enabled mode.

Gorakhpurwalla said OptiNAND also extends the capability of the company’s energy-assisted Perpendicular Magnetic Recording (ePMR) for multiple generations, and that it’s confident that it can deliver 50 terabyte EMR drive in this decade. “There’s a pipeline or roadmap of features, capabilities, and results, and optimizations that come over time that we’ve already planned out.”

Customers needn’t worry about having to customize software to take advantage of OptiNAND, either, he said. Any software, firmware, mechanical and electronics changes are all part of the WD offering and the form factor of the drive still uses existing interface and powers standards. “When you add a memory tier and hence the enhanced capability within the control system of the drive, you also get to manage it appropriately.”

Gorakhpurwalla said WD’s OptiNAND reflects the need of customers to keep up with exponentially growing data and that spinning disk continues to play an important role in conjunction with flash SSDs in the data center. The company’s previously Zoned Storage initiative also saw hard drives as part of a storage design aimed at cloud and hyperscale data centers. That architecture includes shingled magnetic recording (SMR) HDDs combined with the emerging Zoned Namespaces (ZNS) standard for NVMe SSDs to deliver the necessary capacity to meet zettabyte-scale storage demands as well as better endurance and predictable, low-latency QoS performance.

The latest iteration of the non-volatile memory express (NVMe) specification also enables support for HDD with updates to features, management capabilities, and other enhancements required for HDD support as there’s a continued need to accommodate hard drives as SCSI gets left behind in favor of PCIe or NVMe.

By: DocMemory
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