Seagate Exos vs WD Ultrastar: Noise per Part Number, Idle Watts and Cache

Exos vs Ultrastar noise: what each maker's number measures

Both makers print sound figures in bels, and the likeness ends there. Seagate's figures are in its product manuals. Its X24 SATA manual defines them as overall A-weighted acoustic sound power levels with no pure tones, consistent with ISO 7779, taken in essentially free-field conditions over a reflecting plane with the cover facing up. The X24 SAS manual gives sound power measured to the same ISO 7779 specification.

WD's figures are in its data sheets, as one row labelled Bels, typical. We have not found a WD document stating the method behind them: the HC550 to HC590 sheets we hold carry no A-weighting wording and no ISO 7779 reference. Three more things get in the way of a straight reading:

• The second figure is not one test. In Seagate's SATA manuals it is performance seek, with the drive in seek mode only. In the X24 SAS manual it is operating, with no seek figure and no maximum. On WD's sheets it is operating, with no load named beside it.
• The HC590 row runs the other way. That sheet prints Operating/Idle, 3.2/2.5, whilst the HC550, HC560, HC570 and HC580 sheets print Idle/Operating. Read as labelled, 2.5 is the idle figure. We flag the order and do not assume it is right or wrong.
• Idle can move. Seagate warns that offline activity during idle may increase acoustic and power levels to operational levels.

We do not rank these numbers. Setting 2.8 against 2.0 would compare a defined A-weighted measurement with a figure whose method we have not found, and no document we hold tests both makers' drives together. Neither document gives a decibel figure at a set distance, and we hold no source converting one, so we print none.

Exos vs Ultrastar noise per part number: 16TB, 18TB, 20TB and 24TB

Each part number has its own row, with typical values in bels and Seagate's stated maximum in brackets. The second column names the test each maker gives for the active figure. Seagate's rows use its model numbers and WD's use its 0F part numbers.

Some numbers have no row because we have not read the document. We have not opened Seagate's X18 or X20 SAS manuals, so ST16000NM004J, ST18000NM004J, ST18000NM000D and ST20000NM002D are absent. We hold no X16 manual either, so the X16 has idle figures below and no noise row. The HC590 sheet gives only a model pattern at 24 TB, so those four rows take their numbers from WD's en-gb page, and setting a 0F number beside a long string is our reading.

In the X20 and X18 manuals the noise row reads All models, so which part numbers it covers comes from each manual's own model list. The X20 manual is inconsistent on one of them: its cover and the data sheet name ST18000NM004D, whilst its Table 2 prints ST18000NM008D. Both have a row above for that reason.

Read across the four tables, Seagate's rows barely move: the same pair of figures on every SATA manual we hold, and one pair on the X24 SAS manual. WD's idle figure stays at 2.0 until the HC590, and its operating figure is 3.6 on the HC550 and 3.2 on the HC560, HC580 and HC590. Those are movements within each maker's own wording, and they are the only comparisons here we would call safe.

Seagate Exos vs WD Ultrastar at 16TB to 24TB: idle watts and cache

One row per generation and size, naming a SATA number and a SAS number, with watts in the same SATA / SAS order. The exception is the Ultrastar HC560 row, which names no part numbers because its SATA idle figure splits by ALE and BLE models. Each side comes from its own maker's sheet.

The maker's name does not settle the idle rows. At 20 TB the X20's 5.4 W on SATA sits below both HC560 figures, whilst the X24's 6.3 W sits above them. At 16 TB the X16 and X18 are below the HC550 and the X24 is above it. So on power, Seagate Exos vs Western Digital Ultrastar depends on which generation a listing holds. The X24's idle figures run above the older Exos rows on Seagate's own sheets, and our documents give no cause for that, so this page offers none.

Cache follows generation in the same way: an X24 and an Ultrastar both state 512 MB, whilst the X16, X18 and X20 state half that. We hold no workload test of what the gap is worth. The sustained figures rest on different reference points, so a small gap between the makers decides nothing, and operating power has no row because the two makers state it at different loads.

The warranty row ties on the sheets named, and it is a poor basis for a choice in any case: WD says MTBF and AFR do not predict an individual drive's reliability and are not a warranty. Both makers' application lists run through hyperscale, massive scale-out and Hadoop storage, and neither tells you that a drive suits one particular system.

Ultrastar vs Exos on Amazon.co.uk: new listings by price per TB

Each maker has its own table, which takes new rows at any capacity, lowest pounds per TB inc VAT first. They name no winner. A small drive can top either table, so use the capacity column to set rows at the same size against each other. If a table has no row at your size, that side holds none at this moment.

A lowest price per TB is a level and may come from a different size on each side, so we print no percentage between them.

This table leaves out titles carrying NM000C or NM002C, two examples of the endings on Seagate's recertified data sheet, DS39.1-2610US. That sheet also lists NM001C, NM003C and NM004C, which the filter does not catch, and it needs the number in the title, so a recertified drive could still appear: check the part number on each row. Recertified terms have their own page at refurbished Seagate Exos.

This table leaves out HC555 and SS530 titles, which the figures above do not cover. It can still hold HGST-named and other Ultrastar lines with no row above, and for those it gives you price and listing data only. In both tables, the Recording column prints a technology only where a document ties it to the part number, whilst CMR in an Amazon title is a claim by whoever wrote that title.

Exos vs WD Ultrastar: working from the part number

Start from the row you are weighing, not the maker. Find its number in the noise tables and in the idle rows, and note the generation. If the number is on neither, this page has no figures for it. Several generations have their own pages: Exos X24, Exos X18, Ultrastar DC HC550, Ultrastar DC HC560, Ultrastar DC HC580 and Ultrastar DC HC590. Both makers' full ranges are on Seagate Exos and WD Ultrastar.