The hard disk drive industry is gearing its products to meet the needs of high-capacity low-cost storage for enterprise and data center applications as well as some video surveillance applications. SSDs have largely replaced HDDs in personal computing applications and consumer applications such as DVRs are giving way for many consumers to online streaming applications served from content delivery networks associated with content stored in data centers. The Coughlin Associates projections for HDD deliveries is shown below, emphasizing the estimated growth of high capacity nearline storage HDDs.
Although these nearline HDDs are shipping with higher storage capacities, they will also be shipping in higher numbers as estimated demand for HDD storage capacity grows from over 1 Exabytes in 2024 to over 6 Exabytes by 2029. This data growth is due to increased demand for cost effective digital storage to meet the needs of higher resolution data for consumer, industrial and data center applications, particularly various types of AI.
Western Digital made an announcement that it was shipping several new HDDs with higher storage capacities. In particular, the company’s 32TB Ultrastar DC HC690 SMR HDD achieves 32TB of storage capacity on 11 disck using shingled magnetic recording, or SMR, for data center applications. Shingled magnetic recording writes tracks partially overlapping each other to achieve higher areal densities. These drives have up to 257MiB/s sequential reading speeds and can use as little as 5.5W power with idle. They are designed for secondary storage of warm and cold data tiers.
However, shingling the recording tracks results in a slower write process once the HDDs has enough data on it that the drive needs to write over older data. This is because good data to be retained must be moved before a track can be rewritten. Read performance of SMR drives should be about the same as with non-SMR drives. SMR drives are particularly useful in write once, read intensive applications. WDC has indicated that it has high demand for these SMR nearline drives with several customers.
WDC also announced a non-SMR 25TB Ultrastar DC HC590 data center CMR, conventional magnetic recording, HDD. This drive has sustained transfer rates up to 288 MiB/s with as low as 5.6W idle power. These CMR data center drives have similar write and read speeds since they don’t require the data movement required when rewriting SMR HDDs.
The new Ultrastar HDDs include WDC’s ePMR, OptiNAND™, ArmorCache™ and a triplestage actuator (TSA). The company also announced that these Ultrastar HDDs are being qualified in the company’s Utrastar Data60 and Data102 JBOD hybrid storage systems, which can deliver up to 3.26PB of raw storage capacity and feature IsoVibe and ArcticFlow technologies to reduce system vibration and temperature hot spots.
WDC also announced 26TB WD Gold SATA HDDs for system integrators and resellers. These have a five-year limited warranty and are projected to support up to 2.5M hours MTBF, mean time between failures.
Earlier in 2024 Seagate formally announced its 32TB nearline Mozaic HDDs using heat assisted magnetic recording with areal densities of about 1.5Tbpsi, terabits per square inch. These drives do not use shingled magnetic recording and have 10 platters. Shingling these HAMR HDDs would provide greater storage capacity. Seagate also announced it would be shipping 40+TB HDDs by 2026 and 50+TB HDDs by 2028 using HAMR technology. Thus, the Western Digital 11 disk 32 TB SMR HDD will have lower areal density than the Seagate Mozaic drives.
Going to higher disk counts in the same HDD form factor requires thinner disks. Hoya, a glass disk substrate manufacturer has shown higher disk count configurations in the conventional 3.5-inch HDD form factor using thin glass/ceramic substrates at venues such as the 2022 IEEE TMRC conference, e.g. 14 and 24 disk demonstrations. However, achieving such high disk counts requires reducing the thickness of the disks as well as the dimensions of components between the disks.
WDC said that it achieved 11 disks in a conventional HDD form factor by reducing the disk to disk spacing, rather than the thickness of the disks. The WDC 32Tb HDD probably uses aluminum alloy disk substrates like prior WDC data center HDDs. This allows the company to preserve the stiffness of the aluminum alloy disks and thus avoid some mechanical issues.
Note that Seagate’s Mozaic drives use glass substrates that are required to manufacturing the company’s HAMR recording media. These glass substrates are much stiffer than the aluminum substrates, although they likely have a higher cost.
Western Digital’s 32TB Ultrastar DC HC690 SMR HDD has been able to match the storage capacity of Seagate’s 32TB HAMR HDD for data center applications using SMR and an extra disk. The WDC product though sacrifices write performance to achieve this capacity, because it uses SMR, and it is also offering 26TB non-SMR Utrastar data center HDDs.
It is likely that to achieve higher HDD capacities than 32TB with or without SMR, WDC will need to introduce its own heat assisted magnetic recording HDDs, perhaps by 2025. Doing so will enable WDC to continue to compete in the high-capacity data center HDD market with Seagate and Toshiba.
WDC announced that it is shipping SMR data center drives with up to 32TB capacity on 11 disks and non-SMR drives with up to 26TB capacity on 11 disks.