The Robocopy Masterclass: Faster Migrations with Multi-Threading | Lazy Admin Blog

Posted on March 4, 2026 Updated on March 23, 2026

Why use File Explorer when you can use a 128-thread engine?

If you are still using “Drag and Drop” to move terabytes of data, stop. Not only is it slow, but if the network blips for half a second, the whole process fails. Robocopy is built to survive network hiccups and, since Windows 7, it has a “Turbo” button called Multi-threading (/MT).

1. The “Standard” Lazy Migration Command

If you just want to move a folder and make sure all the permissions (ACLs) stay intact, this is your go-to string:

ROBOCOPY C:\sourcefolder C:\destinationfolder /E /COPY:DATS /LOG+:C:\temp\Robocopy_logs.txt

• /E: Copies all subfolders, even the empty ones.
• /COPY:DATS: This is the magic. It copies Data, Attributes, Timestamps, and Security (NTFS ACLs).
• /LOG+: Appends the results to a text file. Always log your copies. If something is missing later, the log is your evidence.

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2. Going “Turbo” with Multi-Threading (/MT)

By default, Windows copies files one by one (Serial). With the /MT switch, you can open up to 128 “lanes” of traffic.

• Default: /MT:8 (8 files at once)
• Aggressive: /MT:32 (Sweet spot for most servers)
• Extreme: /MT:128 (Use this for thousands of tiny files)

Pro Tip: /MT is not compatible with /IPG (which slows down copies to save bandwidth) or /EFSRAW. If you want speed, stick to /MT.

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3. Real-World Examples: Migrating Mapped Drives

When migrating large volumes (like a mapped Y: or Z: drive), you want to use the /MIR (Mirror) switch. This makes the destination an exact clone of the source.

Example: Migrating a Production Volume

ROBOCOPY Y:\lfvolumes\DEFAULT E:\MIGRATE_PRD\E_Drive /MIR /MT:24 /LOG+:D:\Logs\Edrive.txt

Example: Copying a Single Giant SQL Backup (.BAK)

ROBOCOPY T:\ E:\Migrations\ db_backup.BAK /ZB /J /LOG+:D:\Logs\backup.txt

• /ZB: Restartable mode (if the network drops, it picks up where it left off).
• /J: Unbuffered I/O (Recommended for huge files like database backups).

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4. The “Cheat Sheet” of Switches

Switch	What it does
/MIR	Mirroring. Deletes files in destination that no longer exist in source.
/Z	Restartable Mode. Survives network glitches.
/R:n	Number of retries (Default is 1 million—set this to 3 or 5 instead!).
/W:n	Wait time between retries (Default is 30 seconds).
/FFT	Use this if copying to a Linux NAS to avoid timestamp issues.

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🛡️ Lazy Admin Warning:

Be careful with /MIR. If you accidentally point it at an empty source folder, it will “Mirror” that emptiness by deleting everything in your destination. Always test with the /L (List Only) switch first to see what would happen without actually doing it.