SSD Thermal Limits: Controller vs NAND in Benchmarking

This article explores the critical differences between SSD controller thermal throttling and NAND flash thermal sensitivity during computer hardware benchmarking. While the SSD controller actively reduces performance to prevent overheating under heavy loads, NAND flash memory exhibits a complex relationship with temperature, actually requiring moderate heat for optimal write operations while risking data degradation if it gets too hot. Understanding how these two distinct components react to thermal stress is essential for accurately interpreting storage benchmark results and applying proper cooling solutions.

The SSD Controller: Heat Generation and Throttling

The SSD controller is essentially a small processor that manages data flow between the computer and the storage chips. During intensive benchmarking—especially with PCIe 4.0 and 5.0 NVMe drives—the controller works at maximum capacity and generates the vast majority of the drive's heat.

To protect itself from permanent silicon damage, the controller relies on a mechanism called thermal throttling.

  • How it works: When the controller reaches a specific temperature threshold (typically between 80°C and 90°C), the firmware intentionally reduces its clock speed.
  • Impact on benchmarks: Thermal throttling manifests as a sudden, drastic drop in sequential and random read/write speeds. A drive running a sustained write benchmark might drop from 7,000 MB/s to 1,500 MB/s within seconds once the threshold is crossed.
  • Cooling requirement: The controller always benefits from active or passive cooling. Lowering the controller's temperature directly extends the time an SSD can sustain peak benchmark performance.

NAND Flash: Thermal Sensitivity and the Heat Paradox

NAND flash memory, where the data is actually stored, behaves very differently than the controller. NAND does not generate as much heat as the controller, and its reaction to temperature is paradoxical.

  • Writing Data (Warm is better): NAND flash relies on moving electrons through an insulating layer. Higher temperatures make it easier for electrons to pass through this layer, putting less wear on the cells and requiring less energy. Therefore, NAND prefers to be warm (around 40°C to 60°C) during write benchmarks. Over-cooling NAND to sub-ambient temperatures can actually degrade its write endurance and slightly reduce write efficiency.
  • Storing Data (Cool is better): Once data is written, high temperatures cause electrons to leak from the cells, leading to data corruption and bit errors.
  • Impact on benchmarks: If NAND flash gets too hot (usually above 70°C to 85°C), the rate of bit errors spikes. During a read benchmark, the SSD’s error-correction code (ECC) must work harder to fix these errors, which increases latency and lowers read speeds. If the NAND reaches critical temperatures, it will also trigger the controller to throttle the drive to prevent data loss.

Key Differences During Hardware Benchmarking

When running storage benchmarks like CrystalDiskMark, ATTO, or Iometer, distinguishing between controller limits and NAND sensitivity comes down to monitoring and workload types.

1. Sensor Readings Most modern NVMe drives report multiple temperature sensors via S.M.A.R.T. data (viewable in tools like HWiNFO).

  • Sensor 1 (Composite): Usually reflects the NAND temperature or a weighted average of the drive.
  • Sensor 2: Almost always measures the SSD controller. During a benchmark, you will see this sensor spike rapidly, often running 15°C to 30°C hotter than the NAND sensor.

2. Workload Triggers

  • Controller throttling is triggered by high IOPS (Input/Output Operations Per Second) and sustained sequential reads and writes, as the processor is overwhelmed with routing data and calculating parity.
  • NAND thermal limits are usually only reached during prolonged, massive sequential writes where heat from the controller eventually soaks through the PCB (Printed Circuit Board) into the NAND packages.

3. Heatsink Application In extreme benchmarking scenarios, cooling the entire drive uniformly is not always ideal. Enthusiasts often ensure thermal pads make heavy contact with the SSD controller to prevent throttling, while using thinner pads—or no pads at all—on the NAND flash to allow it to stay warm during write-heavy tests, provided the ambient airflow keeps it below its critical 70°C threshold.