Storage demand from AI data centers is drawing increased production investment into the HDD component supply chain. In May 2026, Resonac announced it would increase its HDD recording media output from approximately 160 million disks per year to approximately 210 million. TDK, HOYA, and JX Metals are also expanding capacity for heads, glass substrates, and film-forming materials. However, what's happening is not a broad-based recovery across the entire HDD market, including PC-oriented drives. Investment is concentrated on nearline HDDs—which store large volumes of infrequently accessed data—and on increasing capacity per drive.
Overall Unit Shipments Decline While Nearline Grows
For the fiscal year ending March 2027, TDK forecasts that overall HDD production will decline by about 2%, while nearline HDDs for data centers will grow by 7%. Nearline HDDs are large-capacity drives that remain online at all times but are accessed relatively infrequently, used for storing backup and cloud data. They offer a lower cost per GB than fast SSDs, making them well-suited for retaining infrequently accessed data over long periods.
Component volumes are growing faster than finished products. For TDK's fiscal year ending March 2026, sales of nearline-related HDD heads grew approximately 14%, and suspensions grew 35%. For the fiscal year ending March 2027, the company projects head unit sales will grow approximately 50% and suspensions approximately 22%, with investment going toward HAMR (Heat-Assisted Magnetic Recording) head equipment and expanded suspension capacity. This reflects that HDD manufacturers are increasing the number of disks and heads packed into each drive and raising the recording density of each disk, rather than simply increasing the number of drives produced.
Supply has not kept pace with the surge in demand. In September 2025, TrendForce reported that because major HDD manufacturers had not expanded production capacity in recent years, lead times for nearline HDDs stretched from a few weeks to over 52 weeks. Some cloud providers are considering QLC SSDs even for cold data, but in exchange for roughly 30% lower power consumption than HDDs, they face cost constraints and limited supply of high-capacity SSDs. Even as the supply shortage persists, HDD component makers announced a series of production expansion plans in 2026.
From 160 Million to 210 Million Disks
Resonac's planned expansion amounts to roughly 50 million additional disks, a 31% increase. The company will center this expansion at Resonac HD Singapore, installing equipment on existing floor space and unused areas, while also relocating idle equipment from closed facilities such as its former Taiwan site. Additional lines will be brought online in stages from 2027 onward, based on confirmed demand. By relocating existing assets, the company aims to increase supply while improving capital efficiency.
The figure of approximately 210 million mentioned here refers not to the number of finished HDD units, but to the number of recording media disks used inside them. Because large-capacity HDDs stack multiple media disks, media demand can rise even when drive unit shipments remain flat, simply because more disks are packed into each drive. Furthermore, HAMR uses a laser to locally heat the recording layer, enabling writes to finer magnetic domains. This push toward higher density is also forcing changes in media material design.
Materials used to form the recording layer are also seeing expanded production. JX Metals will progressively increase capacity for magnetic material sputtering targets used in HD media at its Isohara Plant, starting in the second half of fiscal 2026. The company explains that the shift from PMR (Perpendicular Magnetic Recording) to HAMR is driving adoption of new materials. While JX Metals has not disclosed the expansion rate or investment amount, it's clear that the response to supply demand has spread from disk processing steps to film-forming materials.
11-Disk Configurations and HAMR Are Driving Component Investment
HOYA's HDD glass substrate business saw sales grow 25% year-over-year in Q4 of fiscal 2025, and 20% even on a constant-currency basis. A second customer has introduced an 11-disk HDD configuration, boosting substrate demand. HOYA is investing approximately ¥50 billion to build a new facility in Vietnam. Capital expenditure will begin in stages from fiscal 2027, with the facility's full contribution to sales and equipment utilization expected around fiscal 2028.
Glass substrates also serve as a means of fitting more disks into the same 3.5-inch chassis. Toshiba Device & Storage has replaced conventional aluminum substrates with thinner, more durable glass substrates, becoming the first in the industry to verify a 12-disk stack configuration. Combined with MAMR (Microwave-Assisted Magnetic Recording), the company plans to bring 40TB-class data center HDDs to market in 2027. As the number of disks increases from 10 to 12, the number of substrates, recording media, and heads required also rises in tandem.
TDK has been mass-producing MAMR heads since 2021, and at a briefing in May 2026 stated it would begin mass production of HAMR heads two years later. Suspensions are the components that precisely position heads extremely close to the disk surface, and as recording density increases, so do the demands on control precision. Nitto also plans to invest a cumulative ¥43 billion in CISFLEX and high-precision circuits between fiscal 2026 and fiscal 2028. However, this figure also includes capacity expansion for other high-end equipment applications, so not all of it is directed toward HDDs.
The 40TB Race: Three Manufacturers, Three Different Paths to Mass Production
The three finished-product manufacturers are taking different paths toward 40TB-class drives. Between 2026 and 2027, HAMR, ePMR, and MAMR—along with increased disk-per-drive counts—will all enter mass production in parallel.
| Manufacturer | Technology for 40TB-class | Official Roadmap |
|---|---|---|
| WD | Dual approach: 40TB UltraSMR using ePMR, plus HAMR | 40TB products currently under evaluation by two hyperscalers, with mass production planned for H2 2026. HAMR to launch in 2027, expanding to 100TB by 2029 |
| Seagate | HAMR "Mozaic 4+" exceeding 4TB per disk | Up to 44TB certified by two hyperscalers and now in mass production stage. Future goals include 10TB per disk and 100TB drives |
| Toshiba | MAMR with 12-disk glass substrate stack | Plans to bring 40TB-class drives to market in 2027 |
Seagate has already deployed drives up to 44TB into customer environments, while WD is extending its existing ePMR technology while layering in HAMR. Toshiba is increasing capacity through both recording method and disk count simultaneously. Precisely because the technology has not converged on a single approach, component makers must increase volume while supplying materials, heads, and suspensions tailored to each manufacturer's recording method and disk-stacking design.
Conditions for Production Increases to Ease the Supply Shortage
The effects of these production increases will take time to materialize. JX Metals will begin its phased capacity increase from the second half of fiscal 2026, but Resonac's additional lines won't come online until 2027 onward, and HOYA's new facility won't make a full contribution to sales until around fiscal 2028. Even if WD's 40TB products enter mass production in H2 2026, it doesn't mean upstream component supply will increase across the board at the same time.
Each company is proceeding with investment while monitoring demand. Resonac cited market trends and demand as conditions for bringing lines online in stages, and JX Metals similarly described its expansion as phased. If the nearline HDD shortage persists, these investments will be easier to recoup; however, if supply comes to exceed demand, or if the price gap with QLC SSDs narrows, companies may adjust the pace of their expansion.
The timeline for measuring how much the supply shortage eases is clear. WD's 40TB mass production and JX Metals' capacity expansion begin in H2 2026, followed in 2027 by Resonac's additional lines and Toshiba's 40TB-class drives. HOYA's new facility is expected to make its full contribution around fiscal 2028. Beyond whether lead times—which have exceeded 52 weeks—shorten, TDK's head and suspension sales volumes, the pace of Resonac's line launches, and HOYA's new facility utilization rate will each serve as separate indicators of whether the production increases are sustainable relative to demand.