Exos X20: The 20 TB and 18 TB Part Numbers, SAS Options and X18 and X24 Compared

Exos X20 ST20000NM007D and the full 20TB and 18TB grid

ST20000NM007D opens the X20 sheet, DS2080-2111US, dated November 2021: 20 TB, SATA 6Gb/s, standard FastFormat, which ships in 512e and loses all data if switched to 4Kn. The whole generation fits in ten part numbers, because the sheet has only two capacities and only SAS takes the SED-FIPS option.

Small as it is, this grid punishes guessing. The same ending means different things at the two capacities, as the next table shows. ST20000NM002D is the standard 20 TB SAS drive, but ST18000NM002D is the 18 TB SED-FIPS drive. ST18000NM003D is standard 18 TB SATA, but ST20000NM003D is 20 TB SED on SAS. Scaling a part number from one size to the other can land on a different interface and a different security option.

Exos X20 18TB and 20TB: one specification, two sizes

Capacity changes nothing in the rows below. The 18 TB and 20 TB columns print the same figures for transfer, cache, power and weight, so the sheet gives no reason on these rows to pick the smaller size other than needing fewer terabytes. All four columns also read Yes for Conventional Magnetic Recording (CMR).

Because the power figures are shared, 20 TB has the better idle ratio on paper: 5.4 W spread over 20 TB against the same 5.4 W over 18 TB. That is plain arithmetic from one sheet and not a measured running cost.

Seagate's sheet also rates the generation at 2.5M-hour MTBF with a 5-year limited warranty. That is Seagate's statement about the product, not about a particular seller or a used unit. The sheet calls the 20 TB drive 'market-leading', offering 'the highest capacity available'. That wording dates from 2021. The X24 sheet lists 24 TB, so take it as a statement of that moment.

Exos X20 SAS: what the dual-port models add

The SAS side of the sheet has six numbers against four on SATA. ST20000NM002D and ST18000NM000D are the standard drives. ST20000NM003D and ST18000NM001D are SED. ST20000NM005D and ST18000NM002D are SED-FIPS. Against SATA, the idle figure is 0.4 W higher and the random write figure 0.6 W higher. If your backplane and controller are not settled, SAS vs SATA comes first, since the sheet says nothing about any particular chassis.

A footnote on the X20 sheet says SED and FIPS 140-3 validated drives are available through franchised authorised distributors, and may require TCG-compliant host or controller support.

That note creates two checks for anyone who wants a self-encrypting X20. First, ask whether the host or controller supports TCG. Second, ask the seller about supply, because a row in our table cannot tell you whether that seller is a franchised distributor.

Exos X20 vs X18: choosing at 18TB

Set against each other at 18 TB, these sheets are close. Maximum operating power matches on SATA and the idle gap is 0.1 W on SATA or 0.2 W on SAS. The sustained rate is the visible step, at 15 MB/s in favour of X20.

The trap is in the digits. ST18000NM000D is X20 SAS, while ST18000NM000J is X18 SATA. On these two sheets the final letter is what separates the generations, and that observation goes no further than them. Exos X18 has that generation's lower capacities, down to 12 TB.

Exos X20 vs X24: the same speed at 20TB, more cache

Both sheets print 285 MB/s (272 MiB/s), so sustained transfer gives no reason to move between them at 20 TB. What the later sheet changes is cache, doubled to 512 MB, and capacity, up to 24 TB. Its idle power and weight figures are higher too.

Mind the swap: ST20000NM007D is SATA on this sheet and ST20000NM007H is SAS on the other, with 002 doing the reverse. The Seagate Exos range page sets X20 and X24 beside X22, which this page does not cover, and Seagate Exos 20TB follows the one capacity through each generation.

Exos X20 listings on Amazon.co.uk

Below are the Exos X20 rows we match on Amazon.co.uk, priced in pounds inc VAT and marked with their condition, under titles the sellers wrote, so check each part number against the grid on this page. A used row is not proof of a factory-recertified drive.

Other makers at this capacity are a different question, taken up by 20 TB hard drives, and SAS models beyond this one generation sit on 20 TB SAS drives.

In-stock alternatives

None of these is the product this page covers: they are what is in stock on Amazon.co.uk beside it right now. Each row says why it is listed. Check the interface, form factor and part number against your system before buying.