Storage Announcements At Western Digital’s Storage Field Day

At the 2020 Western Digital Storage Field Day (organized by Stephen Foskett), Yusaf Jamal, Senior VP, Devices and Platforms Business said that the drivers for digital storage are 5G and IoT.  Data can reveal what was once invisible, like the 2019 Black Hole Event Horizon images.  Western Digital talked about their developments in digital storage and their applications.  They gave some updates on automotive, gaming and other consumer applications, but this piece will focus on their data center presentations.

Phil Bullinger, Sr. VP and GM of Western Digital’s Data Center Business Unit spoke about providing data infrastructure at the Zettabyte Scale.  He said that this market is estimated to be $3.6 T (trillion) by 2030.  For HDDs this involves Helium filled HDDs, energy assisted recording, advanced suspension mechanics, shingled magnetic recording (SMR) and advance queue management and dual actuator HDDs.  He also said that WDC is shipping its 5^th generation of He-filled HDDS, having shipped more than 50 M units and over 540 exabytes.  As in at the 2019 Western Digital briefing, WDC projects that SMR HDDs will be about 50% of total data center HDDs by 2024, as shown below.

He said that Western Digital is the industry leader for capacity enterprise HDDs with over 80% of 14 TB HDD sales and 56% of all exabytes shipped and over 50% of total units shipped in Q3 2019.  The next generation 18 and 20 TB products move from 8 to 9-platters and include an initial energy assisted magnetic recording.  With higher capacities, fewer HDDs are needed to achieve a given system storage capacity, requiring less rack space and saving energy at data centers. Although SSDs will experience the fastest storage capacity growth in the data center, HDDs will still contain the bulk of data center storage by 2023, as shown below.

Swapna Yasarapu, Sr. Director, SSD Product Marketing, Data Center Devices Business Unit spoke about Western Digital’s Zoned Storage.  WDC’s Zoned Storage initiative includes its shingled magnetic recording (SMR) HDDs as well as its Zoned SSDs.  She said that Zoned Storage enabled various sensor data analysis, AI/ML applications as well as serverless infrastructures.  

She said that it provides a unified approach to manage naturally serialized data at scale and enables predictable performance for cloud-based applications.  With Zoned Storage incoming data and workloads are serialized using data intelligence and a collaboration layer working with software defined storage to provide intelligent data placement via Linux, SMR and NVMe into SMR HDDs or Zoned SSDs.

With zoned storage every virtual machine can be assigned a zone.  Zoned storage, working with RISC-V architectures (see article below) allow reducing overprovisioning for endurance and garbage collection by 10 X and reducing the required DRAM in an SSD by 8 X.  This should result in better performance with lower cost per bit.  Note that Zoned SSDs could also use a mix of different NAND flash types (e.g. MLC and QLC) in different zones and used for different workload tasks.

Carl Che, VP of HDD Technology gave an update on Western Digital’s HDD technology.  Driving factors for HDD development are capacity (and lower $/TB), energy consumption and reliability.  The biggest growing application for HDDs is in high capacity nearline drives used in data centers, particularly as cloud infrastructure. Western Digital’s announced HDD products are shown below.  Carl said that the three pillars for WD’s HDD advances are mechanical innovation, firmware & features and areal density increases.

Last year Western Digital said that it would introduce HDDs using MAMR (microwave assisted magnetic recording) for higher areal density but in it most recent announcement it said that its new 18 and 20 TB 9-platter products are using ePMR, which the company said was a lower risk option to start using energy assisted magnetic recording.  He also said that the company is working on MAMR and HAMR (heat assisted magnetic recording) products.  

The company has not yet announced what sort of energy ePMR is using to enhance HDD areal density.  The company is combining the ePMR in the 18 TB product with shingled magnetic recording to get a 20% capacity improvement (20 TB) for colder storage applications, which WD projects will have the greatest growth in data centers in the coming decade.  Western Digital projects that energy assisted magnetic recording will enable 50 TB non-shingled HDDs and 60 TB shingled HDDs by 2026 as shown below.  Note that MAMR or HAMR-based HDD products are projected for 2022 to 2023 introduction.

Western Digital’s SMR capacity enhancements are accomplished with track-based writes for optimal areal density and a signal format optimized for track-based sequential operations.

Part of the HDD improvement is in a more sophisticated suspension technology.  The WD suspension roadmap (below) shows moving from today’s Dual Stage Actuator (Micro) suspension to triple stage actuator technology in 1H 2020.  This combines the VCM actuator with actuation at the slider/gimbal and also in the suspension/loadbeam as shown below. Carl mentioned that current products have 500,000+ tracks per inch (TPI) with 1 nm positioning accuracy.

Western Digital, like Seagate Technology, has announced that they will be making dual actuator HDDs in 2020.  In addition to making back end testing of high capacity HDDs faster and making system level activities, such as drive rebuilds in an array faster, WDC says that dual actuator drives work better in typical cloud workloads (better IOPS/TB) as the storage capacity increases as shown in the figure below.

Luca Fasoli, VP of Memory Product Solutions, spoke about developments in NAND flash at Western Digital.   Luca told us that NAND bit shipments CAGR is expected to be 36% between 2018 and 2023 (Gartner data).  Western Digital is meeting this demand through higher density flash memory by vertical scaling (number of NAND flash cell layers), lateral scaling (higher planar density) and local scaling (more bits per cell).  Note that the per bit cost reduction with  vertical scaling is generally less for every increase in cell layers, although flash layers at least up to 500 are currently being considered in the future.

He said that in CY2020 the company will release 1XX layer vertical scaled NAND flash (probably 128 layer) and that in the near future this would be higher (probably about 192 layer).  Lateral scaling is accomplished by three methods.  The first is to increase the 3D NAND hole density (smaller diameter holes), the second approach is to go with multi-tiered holes and the third method is to reduce logic and other overhead real estate on the NAND wafers.

Increasing the number of bits per cell provides a scaling benefit but comes with some costs.  The scaling benefit is 100% going from single level cell (SLC) to two level cells (MLC), it is 50% going from MLC to three bits per cell (TLC) and 33% going from TLC to four bits per cell (QLC).  

Going to five bits per cell only provides a 25% scaling benefit.  In addition, the error correction and other processing overhead takes longer and the endurance is less with increasing number of bits per cell (roughly 10 X less endurance for every doubling of the bits per cell).  The figure  below shows the die BW for MLC, TLC, QLC and PLC flash and how this can be improved to some extent with larger page sizes.

Overall, combining vertical scaling, lateral scaling and logical scaling increases the bit density and lowers the cost per bit for 3D NAND flash as shown below.

Scott Hamilton, Sr. Director of Product Management and Marketing for WD’s data center platform business spoke about the companies OpenFlex products, Open Composable API as well as a Kazan network product and the Open Composable Interoperability Lab.   Much of this technology is based upon NVMe over Fabrics (NVMe-oF) that provide low latency, higher performance storage sharing and with the fabric, data access and mobility.  He projected that by 2023 50% of SSD shipments deployed to support primary storage workloads will be based on end-to-end NVMe technology, up from less than 2% in 2019.

The company’s OpenFlex F3100 offers 7.3 M IOPS per rack unit (RU) with 4KiB random read (4.6 MIOPS per RU for write) with a queue depth (QD) of 1 and 39 GB/s per RU with 128 KiB sequential read (33 GB/s per RU with write) with a QD of 320.  An important element in this NVMe-oF solution is the NVMe-oF Bridge from WD acquisition, Kazan Networks, shown below.

He also spoke about how this technology enables an open composable data center infrastructure that turns physical storage, networking, compute and memory devices into logically shared resources.  The company is working with several partners with its OpenFlex architecture to enable this, as shown below.

Richard New, VP of Research talked about the company’s efforts with RISC-V, building an open instruction set computer architecture for use in HDDs and SSDs as well as networks. He also spoke about the CHIPS Alliance to create open hardware for interfaces, processors and systems, as well as open-source design and verification tools.  A number of companies are part of this effort.

He discussed how RISC-V is being used to implement zoned storage that includes shingled magnetic HDDs as well as NAND flash SSDs that gets rid of the flash translation layer in SSDs used to emulate HDDs.  Zoned storage provides direct access to zoned devices.  To make this possible the company and its partners have made significant investments to develop a zoned storage Linux software stack, see below.

One of the more interesting of Western Digital’s RISC-V projects is called opentitan, an open-source silicon project to create a transparent, high-quality reference design for silicon root of trust (RoT) chips.  They are working on this with LowRISC, Google and a coalition of partners.  This can be used to help create secure data infrastructure.  

He also talked about a cache coherent open-source memory fabric called OmniXtend, see below, to provide pools of storage in large memory systems with heterogeneous computing resources.

Western Digital’s Analyst event gave insights into how they see the HDD and SSD market developing as well as their efforts to enable open composable data centers using advanced processor running open RISC-V architectures and Linux software.