Windows Performance Monitor Binary Trace Log Files (.blg)

Bottom Line: It is 100% safe to delete .blg binary performance log files. Performance Monitor (perfmon.exe) generates .blg trace files to record CPU, RAM, and disk performance metrics.

Why Do Windows .blg Performance Log Files Exist?

System administrators and performance engineers use Windows Performance Monitor (perfmon.exe) or Data Collector Sets to log system telemetry.

• Primary Purpose: Diagnostic logging of hardware metrics (CPU utilization, IOPS, page faults).
• Storage Growth: Unattended Data Collector Sets write continuous binary trace files to C:\PerfLogs\System\Diagnostics, consuming 1 GB to 20 GB.

What Happens If You Delete .blg Files?

• System Safety: ✅ 100% Safe to Delete. Core Windows performance is unaffected.
• Log Viewer Impact: You will be unable to view historical trace graphs in Performance Monitor for deleted logs.
• Reclaimed Storage: Reclaims 1 GB to 20 GB of SSD space.

How to Delete .blg Files Safely

:: Delete old Performance Monitor binary log files
del /f /q /s C:\PerfLogs\*.blg

Frequently Asked Questions (FAQ)

How do I stop Performance Monitor from generating huge .blg files?

Open perfmon.exe > expand Data Collector Sets > User Defined > right-click active collector sets > select Stop.