Western Digital Data Center 16-20 TB HDDs

Western Digital announced updates in their nearline data center hard disk drive (HDD) portfolio.  The new sealed helium filled HDDs have capacities of 16 and 18 TB, implement a version of energy assisted magnetic recording (EAMR) and use three pivot points to place heads on the disk surfaces.  These technologies are being used in WDC’s Ultrastar and WD Gold HDDs as well as in the company’s Ultrastar Storage Platforms.  

Many of these developments were discussed at the January 2020 Storage Road Trip visit to WDC.  The 16 and 18 TB drives are now being shipped for revenue and that 20 TB HDDs using shingled magnetic recording (SMR) are shipping for data center qualifications.  WDC said that the 16 and 18 TB HDDs Ultrastar HC550 CMR heads had been shipping to Datto, DDN and Dropbox since March 2020.

The 18 TB HDD, like all of WDC’s nearline HDDs, use aluminum-magnesium alloy disk substrates, which may provide some cost advantages versus glass disks used by other HDD companies.  The 18 TB HDD uses 9 disks and it may be possible to put 10 disks into a conventional 3.5-inch HDD package.  

The energy assistance technology for writing data in these HDDs does not use radiative energy such as from microwaves or lasers (MAMR or HAMR) but instead is using a bias current applied to the head during recording to significantly reduce transition jitter during write and thus allow higher linear density recording.  WDC calls this technology energy assisted perpendicular magnetic recording (ePMR).  

In a white paper WDC explains ePMR,  “During write operations, recording heads do not reach saturation in a consistent way, and thus provide an inconsistent magnetic field on the media. This produces distortion in write currents, which is characterized as ‘jitter’. ePMR applies an electrical current to the main pole of the write head throughout the write operation. This current generates an additional magnetic field which creates a preferred path for the magnetization flip of media bits. This, in turn, produces a more consistent write signal, significantly reducing jitter. When jitter is reduced it is possible to minimize the space between bits written, thus increasing BPI and areal density.”  The image below is from that white paper.

The 18 TB HDD has an areal density (amount of information that can be stored on an area of the disk surface of 1.022 TB/in², while the 20 TB SMR drive with higher track densities has an areal density of 1.16 TB/in².

These HDDs have a triple stage actuator that provides three pivot points to position the heads to write and read on the disk surfaces.  One pivot is the voice coil motor actuator.  This is combined with a milliactuator close to where the head suspension extends from the actuator arm and a microactuator located close to the individual heads.  The image below, from the WDC white paper shows the three actuators.

WDC’s 16 and 18 TB Gold family of HDDs are targeted for channel customers for use in enterprise-class server and storage systems.  They have up to 2.5 M hours mean time between failure (MTBF) and are designed for workloads up to 550 TB per year.

WDC also announced its Ultrastar Data60 and Data 102 JBODs and Serv60+8 storage server using the 16 and 18 TB Ultrastar HDDs as well as SSDs.  These can provide up to 1.836 PB in 4U.  Platforms with upgrades to the 20 TB SMR HDDs are expected next quarter.  WDC sees these products as key elements of next-generation disaggregated storage and software defined storage (SDS) infrastructure.  The Serv60+8 is a high-capacity hybrid storage server that includes computing capability.  These products include WDCs IsoVibe vibration isolation and ArcticFlow thermal cooling technology.

Data center secondary storage is the biggest growth application for hard disk drives.  As shown in the chart below, the total exabytes in capacity enterprise HDDs will be much greater than data center SSDs with a $13B TAM for capacity enterprise HDDs expected by 2023.

Data center high-capacity HDDs are the biggest HDD growth market.  Western Digital is now shipping enterprise grade 16 and 18 TB CMR HDDs with energy assisted magnetic recording with 20 TB SMR HDDs in qualification.