FastCopyCopy speed suddenly dropped? 4 system causes to check
11. Launched from Task Scheduler? It is the I/O priority
Windows assigns background I/O priority to processes started by Task Scheduler. In the task properties, add a "Start program" action that wraps FastCopy with a normal priority, or run schtasks with the /v1 flag removed and set priority manually. GUI-launched copies are unaffected.
22. Antivirus real-time scanning
Security suites scanning every written file can halve small-file throughput. Add an exclusion for FastCopy.exe and for your backup destination folder, then re-measure.
33. Drive health and thermal throttling
Check SMART with CrystalDiskInfo. On NVMe drives, sustained writes can push the controller past 70–80 °C and throttle to a fraction of peak speed — this shows up as "fast for 30 seconds, then slow". Improve case airflow or add a heatsink.
44. Same-drive copies and fragmenting
Copying within one drive is inherently slower (read+write compete for the same medium). Make sure parallel R/W is enabled (default since v5.9.0). On a heavily fragmented HDD, large multi-file sets lose speed — defragment or use an SSD.
Frequently asked
QSpeed is fine for big files but terrible for thousands of small ones — why?
That is per-file overhead, not throughput. Enable parallel R/W, disable per-file verification, and consider copying to a compressed container instead.
QDoes FastCopy slow down over long sessions?
It can look that way when the drive cache fills — the first GBs run at cache speed, then true disk speed. That is the drive, not the software.
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