How SSD Garbage Collection Impacts Hardware Benchmarking

Solid-State Drive (SSD) garbage collection is an essential background maintenance process, yet it frequently compromises the accuracy of computer hardware benchmarks. This article provides an overview of how garbage collection operates and details the specific ways it disrupts both idle and active system states during testing. By consuming power, generating heat, and monopolizing data bandwidth at unpredictable intervals, this background activity skews baseline metrics, causes inconsistent performance results, and requires specific mitigation strategies from hardware testers.

Understanding the Garbage Collection Mechanism

Unlike traditional hard drives, NAND flash memory in SSDs cannot directly overwrite existing data. Data must be written to empty pages, while modified or deleted data is simply marked as "invalid" or "stale." Garbage collection (GC) is the internal process where the SSD controller relocates valid data into new blocks and erases the old blocks containing stale data, freeing up space for future writes. Because erasing blocks is a slow and resource-intensive operation, the drive attempts to perform this maintenance in the background, creating a hidden variable during hardware benchmarking.

Disruption of Idle State Benchmarks

Hardware reviewers rely on idle state testing to establish baseline metrics for system power draw, thermal output, and background resource utilization. However, SSD firmware is specifically programmed to initiate garbage collection the moment it detects the system is idle.

  • Invalidated Power Consumption Metrics: When GC triggers during an idle test, the SSD controller and NAND flash chips become highly active. This causes a sudden spike in power draw, ruining idle wattage measurements and skewing laptop battery life benchmarks.
  • Elevated Thermal Baselines: Moving and erasing gigabytes of data generates significant heat. An SSD performing GC during a supposed idle period will report artificially high temperatures, corrupting the baseline data needed for accurate system cooling and thermal dissipation tests.
  • Blocked System Sleep States: Aggressive background storage activity can prevent the PCIe bus and the CPU from entering deep, power-saving sleep states (C-states). Consequently, the entire motherboard and processor may register higher idle power consumption due to the SSD's internal tasks.

Interference with Active State Benchmarks

Active benchmarks push hardware to its limits to measure maximum throughput, rendering speeds, or system latency. Garbage collection interferes with active states in two ways: either a background GC cycle fails to stop quickly enough when a benchmark starts, or a storage-heavy benchmark fills the drive to the point where it forces immediate, foreground garbage collection.

  • Severe I/O Bottlenecks: When GC runs concurrently with a benchmark, the SSD controller must split its processing power and internal bandwidth between the benchmark’s read/write requests and its own data-shuffling tasks. This leads to a sharp, uncharacteristic drop in sequential and random transfer speeds.
  • Latency Spikes: Program-erase cycles take significantly longer than standard read or write operations. If an active benchmark requests data from a NAND chip currently undergoing a GC erase cycle, the request is queued. This results in massive latency spikes and lower frame-time consistency in gaming or workstation benchmarks.
  • Premature Thermal Throttling: Combining the workload of an intensive active benchmark with the heavy workload of garbage collection rapidly increases the SSD's temperature. This often pushes the drive past its thermal threshold, triggering thermal throttling that tanks performance mid-test.

How to Mitigate Garbage Collection in Benchmarking

To ensure repeatable and accurate benchmark results, hardware testers must control when garbage collection occurs.

  • Enforce Pre-Test Idle Time: After installing benchmarking software or transferring test files, leave the system powered on and completely idle for 30 to 60 minutes. This allows the SSD to naturally trigger and complete its garbage collection cycle before the actual testing begins.
  • Manually Trigger TRIM: Ensure the operating system's TRIM command is enabled and manually run it (via drive optimization tools) prior to testing. TRIM informs the SSD which data blocks are no longer in use, allowing the drive to clear them out efficiently ahead of the benchmark.
  • Use Secure Erase: When conducting pure storage benchmarks, perform a manufacturer-supported Secure Erase between test runs. This resets all NAND cells to a factory-fresh state, completely eliminating the need for garbage collection at the start of the test.
  • Standardize Drive Pre-Conditioning: If testing how a drive handles sustained workloads (steady-state performance), purposefully fill the drive with a standardized amount of data before testing. This forces garbage collection to run predictably, ensuring an equal playing field when comparing different SSD models.