File Transfer Speed: SCP vs. Robocopy vs. Copy-Item

When it comes to transferring large files (10–100 GB) between Windows systems, the tool you choose can have a massive impact on speed, reliability, and security. In this ultimate showdown, we compare three titans of file transfer: the secure and universal SCP (OpenSSH), the multi-threaded powerhouse Robocopy (SMB), and the PowerShell-native Copy-Item (WinRM).

We’ll test them across different network conditions, from a high-speed 10 GbE LAN to a real-world 5G wireless connection, to help you decide which tool reigns supreme for your specific needs.

📊 At a Glance: The Contenders

🏆 Speed Winner (LAN): Robocopy 🔐 Security & Cross-Platform Winner: SCP

🧱 1. Robocopy — The LAN Speed King

Robocopy (Robust File Copy) is a command-line utility that has been a staple of Windows administration for years. It uses the SMB protocol and is optimized for bulk file transfers on local networks.

robocopy "\\server\share" "C:\local\dest" hugefile.zip /MT:32 /Z /J /R:3 /W:5 /LOG+:copy.log

Why It’s So Fast:

• Multi-threaded: The /MT switch allows it to use multiple threads (up to 128) to copy files in parallel.
• SMB 3.x Multichannel: On supported systems, it can leverage multiple network connections for a single transfer.
• Unbuffered I/O: The /J switch reduces I/O overhead for large files.
• Resumable: The /Z switch allows it to resume a transfer if it’s interrupted.

Real-World Test (10 GbE, 50 GB ZIP):

• Robocopy: ~580 MB/s (91 seconds)
• SCP: ~118 MB/s (7.1 minutes)

Requirements:

• An accessible SMB share (e.g., \\server\share).
• Port 445 open between the client and server.
• Valid domain or local credentials.

🔐 2. SCP — The Secure and Reliable Workhorse

SCP (Secure Copy Protocol) is part of the OpenSSH suite and provides encrypted file transfers over the SSH protocol. It is the de facto standard for secure file transfers in the Linux world and is now natively available on Windows.

# Example in PowerShell
scp user@server:/path/to/hugefile.zip $env:USERPROFILE\Downloads\

Performance Tips:

• Compression: Use the -C flag to enable compression, which can help on slower networks.
• rsync for Resumability: For true resumable transfers, rsync over SSH is superior to scp.

  rsync -avz --progress --partial user@server:/path/hugefile.zip ./Downloads/

Why It’s Slower Than Robocopy on a LAN:

• Single-threaded: scp does not use multiple threads for a single file transfer.
• Encryption Overhead: The AES encryption used by SSH is CPU-intensive, which can become a bottleneck.
• No Multichannel: It does not take advantage of multiple network paths.

Despite this, scp is still an excellent choice for 1 GbE networks, where it can often saturate the connection.

🐢 3. Copy-Item (via WinRM) — The PowerShell Native (but Slow) Option

PowerShell’s Copy-Item can be used with a remote PSSession to transfer files over WinRM. While convenient for small configuration files, it is not designed for bulk data transfer.

$session = New-PSSession -ComputerName server
Copy-Item -FromSession $session -Path "C:\share\hugefile.zip" -Destination "C:\local\"

Why It’s So Slow:

• SOAP/XML Overhead: WinRM wraps data in heavy SOAP and XML envelopes.
• No Parallel Chunks: It transfers files in a single, serial stream.
• Not Resumable: If the transfer is interrupted, it must be restarted from the beginning.

Verdict: Avoid Copy-Item over WinRM for any files larger than a few megabytes.

🌐 The 5G Challenge: High Latency, Restricted Ports

Transferring files over a 5G wireless network introduces new challenges: higher latency, potential packet loss, and carrier-grade NAT that often blocks ports like SMB (445).

Typical 5G Network Metrics:

• Download Speed: 100–600 Mbps (12.5–75 MB/s)
• Upload Speed: 20–100 Mbps (2.5–12.5 MB/s)
• Latency: 15–50 ms
• Firewall/NAT: CGNAT and carrier restrictions are common.

On a 5G network, latency tolerance and the ability to work over standard, unblocked ports become more important than raw, multi-threaded throughput.

5G Performance Comparison (50 GB ZIP):

Why SCP Wins on 5G:

• Port 22 is Rarely Blocked: Unlike SMB (port 445), SSH (port 22) is almost universally allowed.
• Latency Tolerance: The SSH protocol is more resilient to the higher latency and jitter of wireless networks.
• Built-in Encryption and Compression: The -C flag helps reduce the amount of data sent over the limited bandwidth.

✅ Final Recommendations

💡 Pro Tip: For the best of both worlds (speed and security), consider running Robocopy over a VPN that encrypts SMB traffic, or tunnel your Robocopy transfer through an SSH connection.

🚀 Conclusion

• Robocopy is the undisputed champion for high-speed file transfers on a local network.
• SCP (and its more powerful cousin, rsync) is the most reliable and secure choice for transferring files over the internet, especially on unreliable or restricted networks like 5G.
• Copy-Item over WinRM should be reserved for small configuration files and not used for bulk data.

By understanding the strengths and weaknesses of each tool, you can choose the right one for the job and ensure your file transfers are as fast, reliable, and secure as possible.