为何Robocopy在网络共享下比Copy-Item慢？需优化参数吗？
Hey there! Let's start by unpacking your test results: you copied from C:\MyStuff to \\somemachine\someshare\mydir, where Copy-Item -Recurse finished in 1.6 minutes, but vanilla robocopy.exe took 2.1 minutes. You’re right to wonder if tweaking Robocopy’s parameters can close (or even reverse) that gap—let’s dive into how to optimize it.
Why Robocopy is slower by default
Robocopy’s default behavior includes extra safeguards that add overhead compared to Copy-Item:
- It verifies file integrity and checks timestamp differences rigorously
- It logs file/directory activity internally (even without a visible log file)
- It copies all file attributes, permissions, and timestamps by default
- It uses single-threaded copying out of the box
Key parameters to speed up Robocopy
Here are the most impactful flags to add to your command:
/MT[:n](Multithreaded copying): This is usually the biggest win. Robocopy can copy files in parallel using multiple threads. Start with/MT:8(8 threads) and adjust based on your network and system resources—avoid going over 32, as too many threads can create overhead./J(Unbuffered I/O): Bypasses the system cache, which is perfect for large file copies over the network. It prevents cache bloat and speeds up direct file transfers./FFT(FAT File Time): Network shares often have tiny timestamp discrepancies (1-2 seconds). Robocopy’s default checks treat these as "different" and recopy files—/FFTrelaxes this check to skip unnecessary work./NODCOPY: Skips copying file attributes (like read-only, hidden) if you don’t need them. This cuts out a small but consistent amount of overhead./NFL /NDL: Disables internal logging of file and directory names. Robocopy does this by default even without a log file, so turning it off reduces background work./E: Equivalent toCopy-Item’s-Recurse—copies all subdirectories, including empty ones (make sure to include this to match your originalCopy-Itembehavior).
Optimized command example
Putting it all together, your command would look like this:
robocopy.exe "C:\MyStuff" "\\somemachine\someshare\mydir" /E /J /FFT /NODCOPY /NFL /NDL /MT:8
Quick notes on testing
Results can vary based on:
- File size distribution (multithreading shines with lots of small files;
/Jhelps more with large files) - Network speed and latency
- System load during the copy
Start with the above command, then tweak parameters (like adjusting the number of threads) to find what works best for your specific setup.
内容的提问来源于stack exchange，提问作者WhiskerBiscuit
