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Robocopy and rsync are the most common tools for NAS migrations, but getting the flags right matters. A missing /SEC flag means your NTFS ACLs don't transfer. Forgetting -H in rsync means hard links become separate files, doubling your disk usage. Using /MIR without /L first can delete files you didn't intend to remove.

This command builder helps you select the right flags for your migration scenario, warns you about dangerous combinations, and explains what each option does. It's free, runs entirely in your browser, and doesn't send any data to our servers.

Common Migration Scenarios

• Mirror a file share: Use /MIR (robocopy) or --delete (rsync) to make the destination an exact copy of the source, including removing files that no longer exist on the source.
• Incremental sync: Use /XO (robocopy) or --update (rsync) to only copy files that are newer on the source. Ideal for ongoing sync before cutover.
• Preserve all metadata: Use /COPYALL or /COPY:DATSOU (robocopy) or -aHAX (rsync) to preserve permissions, ownership, timestamps, and extended attributes. What does /COPY:DATSOU mean?
• Dry run first: Always run /L (robocopy) or -n (rsync) first to see what would change before making any modifications.

What does /COPY:DATSOU mean?

/COPY:DATSOU copies every file property: Data, Attributes, Timestamps, Security (NTFS ACLs), Owner, and aUditing (SACL). It is the same as /COPYALL, while the default /COPY:DAT skips permissions, ownership, and auditing. For the full per-flag breakdown, see Robocopy /COPY:DATSOU explained.

When robocopy and rsync aren't enough

These tools are reliable for same-protocol transfers (SMB-to-SMB or NFS-to-NFS). But when you need to migrate across protocols (NFS to SMB, NAS to S3), verify integrity with checksums, or track progress across terabytes of data, you need a purpose-built migration tool. That's what syncopio is built for.