Exos X18: Part Numbers From 12 TB to 18 TB, CMR on the Sheet, and X16, X20, X24 Compared

Exos X18 18TB: ST18000NM000J and the other 18TB models

ST18000NM000J sits in the first column of Seagate's sheet, DS2045.3-2102US: 18 TB, SATA 6Gb/s, standard FastFormat, shipping in 512e, with all data deleted if it is switched to 4Kn. At the same capacity, ST18000NM001J adds self-encryption on SATA, ST18000NM004J is the standard SAS model, ST18000NM005J is SED on SAS and ST18000NM007J is SED-FIPS on SAS.

On SATA at 18 TB the sheet gives 5.3 W average idle, with 9.4 W and 6.4 W maximum under random 4K/16Q read and write work. The 18 TB SAS column reads 5.6 W, then 9.8 W and 7.0 W. So the same capacity on SAS is 0.3 W higher at idle on paper, and the single port on SATA becomes two.

Exos X18 part numbers across 18TB, 16TB, 14TB and 12TB

Within this grid the endings are unusually tidy. Standard SATA is 000J, SED SATA 001J, standard SAS 004J, SED SAS 005J and SED-FIPS SAS 007J, at all four capacities. Treat that as an observation about this one sheet, not a rule that travels.

One letter shows why. On the X18 sheet, ST16000NM001J is the self-encrypting 16 TB SATA model. On the X16 sheet, ST16000NM001G is the standard 16 TB SATA model. An order that swaps the last character swaps both the generation and the encryption option.

Exos X18 16TB, 14TB and 12TB: what falls with capacity

Idle power on this sheet steps down with size, unlike the X20 sheet, which prints one idle figure per interface at both of its capacities. Moving from 18 TB to 14 TB on SATA saves 0.4 W at idle and 20 g of weight. Sustained transfer does not move: every column reads 270 MB/s (258 MiB/s).

The 16 TB pair sits between them. Its SATA column reads 5.1 W at idle and the same 9.4 W and 6.4 W as the 18 TB SATA model. Its SAS column reads 5.5 W at idle with 9.6 W and 6.7 W, a little under the 18 TB SAS figures. Both 16 TB models weigh 670 g.

The biggest step is at the bottom of the range. At 12 TB on SATA the idle figure is 4.4 W, 0.9 W under the 18 TB model and 0.5 W under 14 TB. SAS flattens out earlier: 14 TB SAS reads 5.0 W at idle with 9.1 W and 6.3 W, and weighs 650 g, so 12 TB SAS differs from it only by 0.1 W on the random write figure.

Is the Exos X18 CMR? What the sheet prints

Yes, as far as Seagate's document goes. The sheet has a row headed Conventional Magnetic Recording (CMR) and it reads Yes for the X18 models. That is a statement about the part numbers in the grid above. The letters CMR in an Amazon title are a seller's claim and prove nothing about the drive behind the listing, so tie any such claim back to the part number.

The other ratings printed for the generation are 2.5M-hour MTBF and a 5-year limited warranty, which Seagate states about the product. That says nothing about a particular seller or a used unit, so ask the seller what stands behind a row. SATA columns list 512 bytes per sector in 512e and SAS columns list 512, 520 and 528, so check what your controller expects before settling on an interface.

Exos X18 vs X20: the overlap is 18TB

The X20 sheet lists only 20 TB and 18 TB, so 18 TB is the one size where this comparison is direct. The later sheet shows 15 MB/s more sustained transfer and slightly higher idle power.

Part numbers are the real hazard here. ST18000NM000J is X18 SATA and ST18000NM000D is X20 SAS, so reading only as far as the digits gets you the wrong generation and the wrong interface. The Exos X20 grid prints that generation's own numbers.

Exos X18 vs X24: 16TB against 16TB

Newer here means thirstier at idle. At 16 TB on SATA, the X24 sheet's figure is 1.2 W above the X18's, and 1.0 W above on SAS. The X24 repeats one idle figure at every capacity down to 12 TB, whereas the X18 sheet lowers it as drives shrink, so at 12 TB the gap grows to 1.9 W on SATA and 1.5 W on SAS. The X24 sheet also lists 512 MB of cache and reaches 24 TB, and Exos X24 sets those points out.

Exos X18 vs X16: 14TB shows the gap

The two generations share 16 TB, 14 TB and 12 TB. At 14 TB on SATA the X18 sheet is 9 MB/s quicker, lists 0.8 W less in its random read figure and is 20 g lighter. The X16 sheet drops further, to 245 MB/s, at 12 TB on SATA, where the X18 holds 270 MB/s.

The 16 TB side of this comparison, with the part numbers either way, sits on Exos X16. Seagate's sheets are 16 months apart: October 2019 for the older generation and February 2021 for this one.

Exos X18 listings on Amazon.co.uk

The table below holds the Exos X18 rows we match on Amazon.co.uk, in pounds inc VAT, with each row's condition shown. Titles are the sellers' own, so check each part number against the grid. A used row is not proof of a factory-recertified drive.

A title reading X18 10TB is filtered out of this table, because the sheet text we hold has no 10 TB column and stops at 12 TB. For a size-first search, 18 TB enterprise hard drives is the broader page, and Seagate Exos puts the whole range in one place.

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.