HAMR Hard Drives: Technology, Reliability and the Seagate Models That Use It

HAMR hard drive technology: how heat-assisted recording works

HAMR stands for heat-assisted magnetic recording. Seagate's own description is short: a small laser diode attached to each recording head momentarily heats a tiny spot on the disk while data is written. Backblaze, in its Drive Stats report for the second quarter of 2026, describes it the same way: a laser briefly heats a microscopic spot on the platter as data is written.

The obvious worry is heat. Seagate says each bit is heated and cools down in a nanosecond, so the HAMR laser has no impact at all on drive temperature. That is the maker's claim; we have not found an independent measurement that tests it.

Seagate sells HAMR under a platform name, Mozaic 3+. Its January 2024 press release states that Mozaic 3+ incorporates Seagate's implementation of HAMR, and its HAMR page presents the platform as the route to areal densities of 3 TB per disk and beyond. The Exos M data sheet ties that drive to Mozaic 3+ and calls it the first hard drive to feature 3 TB per platter.

HAMR changes how bits are written, not the shape of the drive. Seagate says the Exos M keeps the same form factor, interface and cooling as previous generations, and that it blends 90% of trusted, proven components from those generations with the new Mozaic 3+ technology. On the same sheet every Exos M model is also listed with a helium sealed-drive design.

Seagate HAMR hard drive models and part numbers

Two Seagate products are tied to HAMR in Seagate's own documents: the Exos M range for data centres, and the IronWolf Pro 24TB with HAMR, which its data sheet says is designed for commercial and enterprise NAS. The part numbers are what to match against a listing.

The Exos M sheet also gives a 0.35% annualised failure rate rating at full 24x7 operation, 512e sector format and an average idle power of 6.9 W on every model. The IronWolf Pro 24TB with HAMR sheet rates idle noise at 28 dBA, measured in its Idle 1 state.

Seagate's later Exos data sheet, DS2045.4-2511, lists the same four part numbers under the plain Exos name with Mozaic branding, and describes up to 32 TB in an industry-standard 3.5-inch form factor. So a listing may call the same drive Exos or Exos M; the part number settles it.

One wording point matters if you read the sheets yourself. The Exos M data sheet ties the drive to Mozaic 3+ rather than naming HAMR; the HAMR link is made by Seagate's HAMR page and press release. The IronWolf Pro 24TB sheet names HAMR directly and lists it in its Drive Design row as a category beside air and helium.

HAMR hard drive reliability: Seagate's tests and ratings

Reliability was the open question when HAMR was new, and the evidence we have found still comes from Seagate. In a blog post dated 19 January 2024, Seagate reported an in-lab test in which a single HAMR head transferred data for 6,000 hours, equalling 3.2 PB of data, and said this surpassed customer requirements by a factor of 20. It is Seagate's own result, not an independent one.

Seagate explains the benchmark behind that factor. The nearline specification it uses is that a drive will transfer 550 TB per year, or 2,750 TB over five years, and each head is expected to transfer 152 TB reliably over five years. The 3.2 PB head result is set against that 152 TB expectation.

The data sheets add ratings. The Exos M sheet gives every model an MTBF of 2,500,000 hours, a 0.35% annualised failure rate rating at full 24x7 operation and a 5-year limited warranty. The IronWolf Pro sheet says IronWolf Pro drives are rated for 2.5 million hours MTBF and include a 5-year limited warranty. These are maker ratings, not counts of drives that failed in service.

What we have not found is independent field data. Backblaze's Drive Stats report for the second quarter of 2026, covering 1 April to 30 June 2026, explains HAMR in a section of its own, but we have not found an independent failure-rate report for Exos M or IronWolf Pro HAMR drives. Until one exists, any claim that HAMR drives are more or less reliable than earlier drives in service is a claim we cannot support.

Seagate's own case for trusting the design rests on two points already covered: the laser heats and cools each bit within a nanosecond, and the Exos M reuses 90% of components from previous generations. Both are reasons Seagate gives, and both are worth weighing as such.

HAMR vs ePMR vs MAMR: three routes to higher capacity

HAMR is Seagate's route. Western Digital and Toshiba reach today's capacities with different techniques, and a capacity alone does not tell you which one a drive uses.

• Seagate: HAMR, sold as Mozaic 3+, with 3 TB per platter on the Exos M and models up to 32 TB.
• Western Digital: the Ultrastar DC HC590 uses energy-assisted Perpendicular Magnetic Recording (ePMR) and what WD calls the world's first 11-disk HDD platform, for up to 26 TB with CMR.
• Toshiba: the MG10 uses Flux Control Microwave-assisted Magnetic Recording (FC-MAMR) with 10 disks, in capacities from 16 TB to 20 TB.

HAMR is also a separate question from shingled recording. Backblaze notes that the two techniques solve different problems, so manufacturers can combine them. The Seagate HAMR models compared above are not shingled: Seagate lists the Exos M as CMR on all four models, and the IronWolf Pro 24TB with HAMR sheet says it uses conventional magnetic recording.

What comes next: dated capacity statements from Seagate, WD and Toshiba

Plans in this field change quickly, so each statement below carries the date it was made. They are announcements and roadmaps from the makers themselves, and we print each as that maker said it.

Seagate, 3 March 2026: announcing Mozaic 4+, the next generation of its Mozaic platform, Seagate said its Mozaic 4+ hard drives supporting capacities up to 44TB are now shipping in volume to two leading hyperscale cloud providers, that these qualifications reflect production-scale deployments in hyperscale environments, and that broader availability is planned as production continues to scale. The release names no retail availability. It also sets out a roadmap from today's 4+TB per disk towards a future 10TB per disk, enabling hard drive capacities of up to 100TB. That is a roadmap statement, not a product.

Western Digital, 3 February 2026: WD said its HAMR HDD qualifications were underway with two hyperscale customers, with ramp production in 2027, and that HAMR will scale to 100TB by 2029. In the same announcement it said its 40TB UltraSMR ePMR drive, a shingled design rather than HAMR, was in qualification with two hyperscale customers. A WD blog post published the same day says the point where HAMR becomes the optimal choice emerges at 40TB and above.

Toshiba, 14 May 2024: Toshiba said it planned to start shipping test sample HDDs of 28 to 30TB with HAMR technology in 2025. We have not found a later Toshiba document confirming whether those samples shipped. Toshiba, 14 October 2025: in a release on verifying 12-disk stacking for hard drives, Toshiba said it was targeting launch of next-generation 40TB-class HDDs in 2027, a target the release frames within its MAMR roadmap.

The three statements are not one plan. Seagate says Mozaic 4+ drives of up to 44TB are already shipping in volume to hyperscale customers. WD puts the point where HAMR becomes optimal at 40TB and above, with HAMR ramp production planned for 2027. Toshiba's 40TB-class target for 2027 sits within its MAMR roadmap. None of that changes Seagate's current data sheets: the HAMR part numbers on them are still the five compared above.

HAMR hard drive price in the UK

This guide prints no launch price and no list price. We have not found a Seagate document that states a UK price for a HAMR drive, and a figure seen only in a news summary is not one we repeat.

Live Amazon.co.uk prices, in pounds inc VAT, are on our capacity pages: 24TB hard drives, 28TB hard drives and 30TB hard drives. Seagate's wider range is on Seagate Exos, and IronWolf Pro 24TB covers that capacity of the NAS line. A HAMR model may not be in stock when you look, so those tables can show other drives at the same capacity.

Capacity is not proof of HAMR. At 24 TB, the Exos M ST24000NM001K and the IronWolf Pro ST24000NT031 are tied to HAMR in Seagate's documents, but other 24 TB drives exist, and we have not found a Seagate sheet that states HAMR for IronWolf Pro models above 24 TB, so we do not call them HAMR. Match the full part number in the listing title against the comparison above before you rely on it.

Before you buy a Seagate HAMR hard drive

• Find the full part number in the listing and match it to one of the five above. A title that says only 24TB Exos or IronWolf Pro does not settle it.
• Check the format your system needs: the Exos M ships as 512e on every model.
• Seagate says the Exos M keeps the same form factor, interface and cooling as earlier generations. Whether a given server, controller or NAS addresses a drive of that size is a question for its maker.
• Read reliability figures as ratings: MTBF, AFR and warranty are Seagate's terms, and we have not found independent field data for these models.

The first route to market was not retail. Seagate said in January 2024 that Exos 30TB-plus products were shipping in volume that quarter to hyperscale cloud customers. Its March 2026 release says Mozaic 4+ drives are shipping in volume to two hyperscale cloud providers, with broader availability planned.