What are the 3 temperatures (composite and sensors) reported by a WD_BLACK SN770 NVMe?

Question

I have a WD_BLACK SN770 SSD NVMe that may be running too hot under load.

So to monitor it, I installed Western Digital Dashboard and it reports 3 temperatures:

Libre Hardware Monitor reports 3 temperatures too:

Western Digital Dashboard shows the Composite temperature on the "State" dashboard, so it looks like this is the temperature that is used to detect overheating.

The question: What are "Composite Temperature", "Temperature Sensor 1" and "Temperature Sensor 2"? I can't find any explanation anywhere. I would like to know where the probes located on the NVMe device.

Answer 1

Source: https://borecraft.com/files/intro-composite-temp-white-paper-345213.pdf

Composite Temperature is a single, normalized temperature value that considers input from multiple temperature sensors ... while reporting to the host a single Composite Temperature value for thermal management.

... does not necessarily represent the actual temperature of any physical point within the SSD.

Composite Temperature works by monitoring multiple temperature sensors at regular intervals and comparing each current sensor value to a pre-set maximum value.

(The) NVMe recommendation of 70C is referred to as WCTEMP or Warning Compositive Temperature Threshold.

You can see that it's not a temperature in the traditional sense, but a reference that informs the host system or user ... before it (the SSD) reaches a thermal limit.

More info in the NVMe specifications: https://nvmexpress.org/wp-content/uploads/NVMe-NVM-Express-2.0a-2021.07.26-Ratified.pdf

I tried locating some NVMe SSD's schematic or some manufacturer information, but that seems to be very rare:

That leaves the option to look at some NVMe SSD (CORSAIR Force MP510 in this case) and try locate SMD sensors to get their actual locations which I did for some random SSD. In this example the sensor seems to be located closely to a NAND chip:

For your particular SSD you'd need a high resolution picture from both sides, or examine the SSD under a microscope. For this purpose a digital microscope may be easiest. Use this as reference for example.

I am not certain all sensors may actually be in the form of a separate SMD component.

It still leaves the question what Sensor corresponds with Sensor 1, Sensor 2 etc.. My best guess would be (I know you're not asking for guesses):

Temp   - Composite
Temp 1 - Controller
Temp 2 - NAND or board SMT (?)

Answer 2

The composite temperature value takes into account multiple thresholds and sensors on the disk, and its purpose is to generate one number which gives you a relative idea of how hot the drive is running. The manner in which this value is computed is implementation specific and may not represent the actual temperature of any physical point in the NVM subsystem. The value of this field may be used to trigger an asynchronous event in the firmware.

Source : Kingston SMART Attribute Details.

This composite temperature value is taken as decisive in terms of warranty claims, so is the most important number.

The values of the other sensors are taken into account when computing the composite temperature. Unfortunately, WD does not make available a circuit diagram of the disk, so we cannot say where sensors 1 and 2 are positioned.

As regarding the temperatures you're seeing, they are well within the operating parameters of the disk.

The WD Black SN770 SSD Review has this to say about the disk's temperatures under load:

If WD’s Dashboard software is reading the sensors in the drive correctly, however, the SN770 does get pretty toasty under a sustained load, at least when Game mode is enabled. We saw a peak temperature of 81°C after two complete writes across the entire capacity of the drive in that configuration. With Game mode disabled though, which is how the drive is configured by default, temperatures are a bit lower. Performing the same test with Game mode disabled resulted in a maximum temperature of 75°C. With temps like this, if you’re going to stick the SN770 in a motherboard that doesn’t have M.2 heatsinks, make sure there’s good air-flow over the drive. Enabling Gaming Mode on the SN770 essentially disables any power-saving / sleep features, so the drive is always at the ready. Toggling the feature on and off had only minimal impact on the benchmarks we ran (as you’ll see a little later), but may theoretically minimize stutter or occasional hiccups in games that don't access the storage subsystem very often.

Typically, an SSD will report such a value and begin throttling above 70C, often around 75C, with a later heavier throttling state before reaching a maximum near 85C.

Answer 3

A quick look into the drives datasheet reveals the specified operating temperature for the drive:

OPERATING SPECIFICATIONS:
■ Operating Temperature:
32ºF to 185ºF (0ºC to 85ºC)
■ Non-operating Temperature:
-40ºF to 185ºF (-40ºC to 85ºC)

60°C is well in spec. Better cooling won't hurt for prolonging the lifetime, so you could simply add a better fan or a heat spreader