WD Ultrastar DC HC560 20TB: Part Numbers and the AL and BL Variants

WD Ultrastar DC HC560 0F38785: the AL and BL SATA variants

The 20 TB label hides a split on this model. WD lists four SATA model numbers, two starting WUH722020AL and two starting WUH722020BL, and its footnotes attach different power and write figures to each pair. If you searched 0F38785, you want the right-hand column: WD ties that code to WUH722020BLE6L4.

The write row is the bigger gap. With write cache disabled, the BL models are rated 110 IOPS above the AL models, and they lose nothing when the cache setting changes. Random read stays at 212 IOPS across the sheet, so this gap is about random writes only. The idle saving is modest: 0.3 W over a full year of idling comes to about 2.6 kWh per drive, by our arithmetic.

We have not found a WD document that defines the B in these numbers, so we do not call BL a revision, a later build or a replacement. All this page can say is that the sheet's figures differ by model number, and they apply only to the numbers the footnotes name.

WD Ultrastar DC HC560 20TB SATA or SAS: part number map

SAS has no AL pair on this sheet: both of its model numbers start WUH722020BL. WD's model-number key gives a final 1 as SED and a final 4 as Base SE, and the sheet labels 0F38651 SED and 0F38652 Base SE, so we paired them on that basis. The SATA pairs need no inference: a footnote names each one. SAS copies the BL write figures yet idles like the SATA AL pair, so neither column wins on every line. A faster interface limit changes nothing about the 291 MB/s the disk itself can sustain.

Ultrastar DC HC560 datasheet: OptiNAND and the ratings

The sheet is dated July 2022, document D018-000383-AA02. WD describes this model as the first implementation of the capacity-enabling features of OptiNAND, reaching 20 TB on nine disks at 2.2 TB per platter in CMR format. It also lists ePMR and a seventh-generation HelioSeal design, with self-encrypting options.

OptiNAND is easy to misjudge from the word NAND. WD states plainly that it is not a hybrid technology: an iNAND flash device sits alongside the spinning media and takes metadata that has been offloaded to it.

• Form factor and speed: standard 3.5-inch, 7200 RPM.
• Data buffer: 512 MB, part of it used for firmware.
• Average latency: 4.16 ms.
• Workloads: up to 550 TB per year.
• MTBF: 2.5 million hours, projected. AFR: 0.35%.
• Limited warranty: 5 years, as the sheet words it. We have not found a WD statement of UK terms for the HC560.
• Maximum weight: 690 g. Z-height: 26.1 mm.
• Noise: 2.0 Bels idle, 3.2 Bels operating.
• Areal density: 1131 Gbits per square inch.

Ultrastar 20TB: HC560 or HC555

WD's later HC555 sheet, from November 2024, also lists 20 TB, and its model format starts with the same digits: WUH722020CL. So the letter after 020 is what separates them. AL and BL belong to the HC560 sheet, CL to the HC555. A listing that says only WUH722020 has not told you which drive it is.

Set side by side, the older sheet wins 6 MB/s of transfer and the later one wins at idle against either HC560 SATA pair. We found no OptiNAND mention in the HC555 sheet text, and that is as far as we go: it does not tell you how the drives compare in service. The wider 20 TB field, other makers included, sits under 20 TB hard drives.

Going up a capacity, the HC570 is the 22 TB, ten-disk drive WD calls its second-generation OptiNAND platform. Its sheet names ArmorCache; we found no mention on the HC560 sheet. It keeps the same 291 MB/s and 550 TB per year.

Ultrastar DC HC560 20TB price on Amazon.co.uk

This table is where the price sits: each row carries its own, in pounds sterling inc VAT, read from Amazon.co.uk.

The match works on the Amazon title: the family name, one of the sheet's part numbers or the WUH722020 prefix, leaving out titles that name the HC555 or WUH722020CL. A listing titled only as a 20 TB Western Digital drive can therefore be missing from it. Before relying on any row, compare its number with the two grids above. If that number is not among the six models or six short codes WD prints, the AL and BL figures do not describe it.

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.