U.3 SSD Buying Guide: U.3 vs U.2, Tri-Mode Bays, Sizes and UK Prices

U.3 SSD connector: the same SFF-8639 as U.2, a different rule

Quarch describes U.3 as a tri-mode standard that builds on the U.2 specification and uses the same SFF-8639 connector, the name SNIA gives as U.2's former title. It names the Host Port Type pins, HPT0 and HPT1, as part of how the mode is signalled. Since the connector is shared, its name will not tell you which you are holding. The drive's own sheet will: Micron's 9400 chart reads U.3/U.2, 2.5 inch, 15 mm, SFF-8639, and Kioxia's CM7 briefs read SFF-TA-1001 conformant (U.3).

What this rests on: one Quarch article from April 2019 and one Lenovo product guide. We have not read the SFF-TA-1001 specification, and a Broadcom document that could have been a second source went unread. Treat the table as direction, not as a promise about your hardware.

A U.2 drive is not a U.3 listing, and this page does not treat it as one. If the documents for a particular U.3 bay do list U.2 drives, those documents govern, and those rows are on U.2 SSDs, along with that form factor's dimensions and its comparison with M.2.

NVMe U.3 SSDs in a tri-mode bay: what one server documents

Lenovo's guide to the ThinkSystem SR650 V3 gives the clearest working example we hold. It says the RAID 940 and RAID 9450 adapters support NVMe through a feature named Tri-Mode support, which enables NVMe U.3 drives at the same time as SAS and SATA drives, that tri-mode requires an AnyBay backplane, and that in this configuration only NVMe drives with a U.3 interface are supported. As an alternative to tri-mode, it says the RAID 9450-32i adapter supports connectivity to either NVMe U.2 and U.3 drives. So on this server U.3 is a requirement of the tri-mode configuration, not of every NVMe setup. It is one server, so read your own machine's documents for its version of that sentence. Other backplane types are set out on enterprise SSD.

U.3 availability: what Micron and Samsung say on their own sheets

Micron's 7450 specification, Rev. C of February 2026, records 'Removed U.3 form factors.' in its revision history, and that sheet now lists single-port M.2 and E1.S. We have not found a Micron document explaining why. So a 7450 row whose title says U.3 is a part the current sheet no longer covers: match its part number before you rely on any figure.

Samsung's PM9A3 white paper says its E1.S, E1.L and U.3 versions perform similarly to U.2 products and are provided to contracted and selected OEM companies, and that Samsung will not provide detailed numbers for them. We read that as an OEM route rather than a general retail one. Take the same care with a U.3 PM9A3 row, since the numbers you find may be for the U.2 drive.

Other sheets list it. Kioxia's tech brief lists the CM7 Series in U.3 2.5-inch and E3.S. Micron's 9400 specification, Rev. B of April 2025, lists a U.3/U.2 drive. Samsung's PM1743 white paper says that PCIe Gen5 drive dynamically supports both U.2 and U.3. The lesson for a buyer is to read the revision date on the sheet as well as the figures on it.

U.3 SSD 8TB, 16TB and 30TB: the capacities on the sheets

These sheets hold no drive of exactly 8, 16 or 30 TB: those searches land on 7,680 GB, 15,360 GB and 30,720 GB. The endurance grade changes what is on offer. Kioxia's briefs give the CM7-R 1 DWPD and the CM7-V 3 DWPD, each with a 5-year warranty on that product, and the CM7-V stops at 12,800 GB. So a 15,360 GB Kioxia CM7 is the read-intensive line on these documents. The warranty line says nothing about any Amazon.co.uk listing.

U.3 SSD speed: the label does not set it

The sheets put these two drives a PCIe generation apart. Kioxia's CM7-R is PCIe 5.0 and quotes up to 14,000 MB/s sustained sequential read, in single-port x4 mode. Micron's 9400 is PCIe Gen4 and quotes up to 7,000 MB/s. That is twice the figure on our arithmetic, for reasons that have nothing to do with the letter U. These are makers' numbers and not our tests.

Nor does U.3 settle the port count. Kioxia's brief states a dual-port design for the CM7-R, where Micron's sheet lists a single port x4 for the 9400. Power is a further line to read: the CM7-R brief gives 25 W and 22 W typical active power, and the Kioxia CM7 page sets out which capacities take which figure. Kioxia lists PLP for the CM7-R and Micron states full power-loss protection for the 9400, and both of those need confirming for your part number.

U.3 SSD NAS: what we could and could not find

We have not found a NAS maker's document listing U.3 drives. The NAS example we hold is a U.2 one, on the U.2 page. So we name no NAS here, and a U.3 row should be taken to a NAS maker's own compatibility list before you buy it for that purpose.

U.3 SSD price: live listings on Amazon.co.uk

The table holds 5 listings right now. Lowest per TB: £825.09/TB. Prices are pounds sterling inc VAT, as Amazon.co.uk lists them at the time shown at the top of the page. The table takes listings recorded as NVMe with a U.3 form factor and nothing else, so a U.2 row never appears here. It can run short or empty, and a dash means no row at the time shown.

How to choose a U.3 SSD

• Read your backplane's documents first. A tri-mode setup like Lenovo's may require U.3, while a plain U.2 host relies on backward compatibility as Quarch described it in 2019.
• Check the sheet's revision. Micron's current 7450 sheet no longer lists U.3.
• Check the route. Samsung describes its U.3 PM9A3 as going to selected OEM companies.
• Pick the grade before the size, because Kioxia's CM7-V stops at 12,800 GB.
• Read the PCIe generation and port count from the sheet, as U.3 tells you neither.
• Read the Condition column and the seller's wording on Amazon.co.uk, then press Buy on Amazon once the part number matches.