18TB SAS Drive: Exos X18 and X20, Ultrastar HC550, Toshiba MG09 and MG11 Compared

18TB SAS HDD part numbers by maker

Three makers account for the five lines. At this capacity the part number does the identifying, because Seagate has two generations at the same size and so does Toshiba. A listing that says only 18TB SAS could be any of them.

The Seagate pair needs the closest reading. The X18 sheet's column headings put ST18000NM000J under SATA 6Gb/s and ST18000NM004J under 12Gb/s SAS. The X20 sheet puts ST18000NM003D under SATA and ST18000NM000D under SAS. So ST18000NM000J and ST18000NM000D share every digit and differ only in the last letter, and that one letter changes both the generation and the interface: the J is the X18 in SATA, the D is the X20 in SAS.

Seagate's X18 sheet also separates the two interfaces by port count: its interface ports row reads Dual for the SAS columns and Single for SATA. That is one more row to set against a listing, but the part number remains the safer test, because a title can leave the port count out.

18TB SAS drive price on Amazon.co.uk

This table holds 5 listings right now. Prices are pounds sterling inc VAT, and new and used offers sit side by side, so read the condition on each row. The Recording column shows CMR only where a maker document for that part number supports it; CMR in a listing title is the seller's claim.

18TB SAS Seagate Exos: X18 or X20

Both Seagate generations make an 18 TB SAS drive, so a search for an 18TB SAS Exos can land on either: ST18000NM004J on the X18 sheet, ST18000NM000D on the X20 sheet. Treat them as two products, and check the number your listing prints against the sheet for that generation.

On recording technology the two sheets agree. The X18's Conventional Magnetic Recording row reads Yes in every column, and the X20's reads Yes for all four of its models, ST18000NM000D among them. So whichever Seagate generation you end up with, the sheet for its SAS model states CMR.

On the X20 sheet the 18 TB pair shares its standard-model row with the 20 TB pair, ST20000NM007D and ST20000NM002D. If you are weighing the step up, the 20TB SAS drive page compares that capacity, and the Exos X18 page covers the older generation at every size.

Toshiba 18TB SAS: MG09 or MG11

Toshiba also has two generations at this size, and the MG09 gives you a sector-format choice the MG11 row does not. Toshiba's MG09 model table lists MG09SCA18TE as SAS-3.0, 18 TB, 512e and MG09SCA18TA as SAS-3.0, 18 TB, 4Kn. The MG11 overview lists MG11SCA18TE as SAS-3.0, 18 TB, 512e.

So the last letter is the sector format: a listing titled MG09SCA18TE is the 512e version, and MG09SCA18TA is the 4Kn one. If your controller or array expects 4Kn, that letter decides the purchase. The Toshiba MG09 page covers that generation at every capacity.

Both overviews state CMR. The MG09 overview says the series provides 18 TB of conventional magnetic recording (CMR) capacity, and the MG11 overview describes Conventional Magnetic Recording for broad compatibility. Both give an industry-standard 3.5-inch, 26.1 mm height form factor.

WD Ultrastar HC550 18TB SAS

WD's HC550 sheet prints WUH721818AL5200 in its model numbers row and describes 14/16/18TB capacity in a standard 3.5-inch form factor. The idle row gives 5.8 W for the SAS model, which is 0.32 W/TB by our division. WD also states that CMR technology works with all capacities in the family.

The sheet prints a 5-year limited warranty. That is WD's term for the drive as a new product, and it does not tell you what a particular listing carries, least of all a used one. The Ultrastar DC HC550 page sets out the whole family.

Before you buy an 18TB SAS drive

Check the controller first: Seagate's knowledge base says SAS drives cannot be plugged into SATA controllers. The rest of that rule is on the 20TB SAS drive page and in SAS vs SATA, and the 16TB SAS drive page sets out the lines one step down.

Buying as an individual from a trader brings Part 1 of the Consumer Rights Act 2015 into play, and with it a short-term right to reject a faulty drive that ends after 30 days in the standard case. A company buying drives for its own servers is not a consumer under the Act's definition, which covers an individual acting wholly or mainly outside their trade, business, craft or profession.