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Robocopy’s /MIR switch can delete files and folders from the destination. Microsoft defines /MIR as /E plus /PURGE: it makes the destination match the source by removing destination items that are missing from the source. To avoid surprises, verify both paths, preview the operation with /L, inspect the log, and only then remove /L for the real run. If destination-only files must be retained, use /E instead of /MIR, with /XX where appropriate.
What Robocopy /MIR really does
Robocopy is built into Windows and copies files and directory trees from a source path to a destination path. The command’s direction matters: the first path is the source, and the second is the destination.
/MIR means “mirror.” Microsoft documents it as equivalent to /E plus /PURGE. /E copies all subdirectories, including empty ones. /PURGE deletes destination files and directories that no longer exist in the source. Therefore, a mirror is not a protected backup: a file that exists only in the destination is a candidate for deletion when the command runs. See Microsoft’s Robocopy command reference.
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The word “mirror” describes synchronization, not historical retention. If a file is deleted from the source and you run /MIR, the corresponding destination copy is normally treated as an extra and removed. If a file is renamed, the old name can be purged and the new name copied. A mirror therefore preserves the current shape of one tree; it does not preserve every earlier state of that tree.
Does Robocopy /MIR delete files?
Yes. It can delete files and directories from the destination when they are absent from the source. The deletion applies to destination-only items within the scope of the command, including items that were placed there independently of the source. It does not mean Robocopy deletes every destination file: files that correspond to source items are copied or updated according to their differences, while extras are the items targeted by purge behavior.
That distinction is why the source and destination must be identified before execution. If the paths are reversed, the wrong folder becomes authoritative. With /MIR, that mistake can make the intended source tree look like destination-only content and expose it to deletion.
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The safe mirror workflow
Use this process whenever deletion at the destination would be costly.
- Identify the authoritative folder. Write down the complete source and destination paths. Decide which location contains the files that should win if the two trees differ. Do not assume that a path copied from an example applies to your computer.
- Check the destination’s contents. Open the destination in File Explorer or list it from the command line. Identify any destination-only files or folders that must survive. If any must remain, plan to use a non-purging command rather than
/MIR. - Preview the mirror. Add
/Lto the intended command and write the output to a log. For example:
robocopy "C:Source" "D:Backup" /MIR /L /LOG:"C:LogsRobocopy-preview.log"Replace every example path with a real path from your environment. Check quotation marks, drive letters, spelling, and the location where the log will be written. Quoting is especially important for paths containing spaces.
- Read both the console output and the log. Confirm that Robocopy identifies the expected source and destination roots. Look specifically for destination-only files and directories that the preview says would be removed. Check exclusions as well; an excluded item will not participate in the copy or mirror operation.
- Change the command if the plan is wrong. If anything that must be retained is listed for deletion, remove
/MIRand use a copy-oriented command such as/E, optionally with/XX. Preview that revised command again. - Run only after the preview is acceptable. Remove
/L, retain a log switch, and execute the command from an account with the required access to both locations. - Review completion status. Keep the log and interpret Robocopy’s return code. A code of 8 or higher indicates that at least one failure occurred, even if many files were copied successfully.
/L is a list-only mode. Microsoft states that, with /L, files are not copied, deleted, or timestamped. It is a preview of the planned operation, not a backup and not a rollback mechanism. Remove it only after the displayed changes are understood. Microsoft also describes logging as a way to review integrity after the run; see the Azure Files Robocopy migration guidance.
Run the preview against the same paths, switches, exclusions, and log location you intend to use for the real operation. Changing a switch after reviewing the preview can change the plan. A preview made with /E, for example, does not prove what a later command using /MIR will delete.
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Choosing a command that matches your goal
| Goal | Typical switches | Effect on destination-only items | Use when |
|---|---|---|---|
| Exact directory-tree mirror | /MIR |
Can delete them | The destination must match the source and removals are intentional. |
| Recursive copy/update | /E |
Retains them by itself | You want subdirectories, including empty ones, copied without adding purge behavior. |
| Copy while explicitly excluding extras from deletion | /E /XX |
Excludes destination-only files and directories from deletion | You want recursive copying but cannot allow a strict mirror. |
| Preview any of the above | Add /L |
No files are copied or deleted | You need to inspect the plan before making changes. |
/XX changes the result from an exact mirror: destination extras are excluded rather than removed. Microsoft’s reference specifies that excluded extra files are not deleted. Do not call an /E /XX result a strict mirror, because the destination may contain content absent from the source.
/E and /MIR are often confused because both recurse through subdirectories. The difference is purge behavior. /E adds directories, including empty ones, and updates files without itself requesting deletion of destination extras. /MIR adds that deletion behavior through /PURGE. Choose based on whether the destination is a disposable replica or a location that accumulates independent content.
Preview commands you can adapt
Preview an exact mirror
robocopy "C:Source" "D:Backup" /MIR /L /LOG:"C:LogsRobocopy-preview.log"This lists additions, updates, mismatches, and destination items that the real mirror would purge. It does not make those changes while /L is present.
Preview a non-purging recursive copy
robocopy "C:Source" "D:Backup" /E /L /LOG:"C:LogsRobocopy-preview.log"This copies the tree recursively when run without /L, including empty directories, but /E alone does not invoke purge. Existing destination-only content is not targeted for deletion by that switch.
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robocopy "C:Source" "D:Backup" /MIR /LOG:"C:LogsRobocopy-run.log"Use /LOG+: instead of /LOG: when you want to append to an existing log rather than overwrite it:
robocopy "C:Source" "D:Backup" /MIR /LOG+:"C:LogsRobocopy-history.log"These are syntax templates, not universally safe commands. The correct paths, permissions, exclusions, filesystem behavior, and retention policy depend on your environment. A separate physical drive can be used as a destination, and Microsoft also documents Robocopy workflows for Azure Files, but neither a second drive nor cloud storage changes what /MIR does when aimed at that destination.
How to read Robocopy’s return codes
Robocopy’s exit code is not a simple “zero means good, nonzero means bad” scheme. Codes below 8 describe combinations of copying, mismatches, and extra items; codes 8 and above indicate at least one failure.
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| Code | Microsoft’s documented meaning | What to do |
|---|---|---|
| 0 | No files were copied, and there was no failure or mismatch. | Confirm that an already synchronized tree was expected. |
| 1 | All files copied successfully. | Review the log for the files changed. |
| 2 | Destination has extra files or directories. | Decide whether extras are acceptable or indicate an incorrect source, destination, or switch choice. |
| 3 | Files were copied and destination extras exist. | Check whether the extras should remain. |
| 5 | Files were copied and mismatches exist. | Investigate mismatched attributes, timestamps, or content as appropriate. |
| 6 | Extras and mismatches exist, but no files were copied. | Review the log and determine whether the differences are intentional. |
| 7 | Files were copied, with mismatches and extras. | Review all listed differences before treating the run as complete. |
| 8 or higher | At least one failure occurred. | Treat the run as unsuccessful until the log identifies and the failed items are addressed. |
Interpret the code together with the command’s purpose. For example, a code reporting extras may be expected during a non-purging copy, while the same result may signal that an exact mirror was not achieved. Automation should generally treat 8 or higher as a failure condition, while recording lower codes for later review rather than assuming every nonzero value is an error.
Limit the operation with exclusions
Robocopy can narrow the scope, but every exclusion also means that content is intentionally omitted from the operation. Preview exclusions before a real run.
/XDexcludes matching directories./XFexcludes matching files./XJexcludes junction points. Junctions are normally included by default, so this switch can prevent traversal into linked directory locations.
For example, a preview that excludes a cache directory and temporary files could look like this:
robocopy "C:Source" "D:Backup" /MIR /XD "C:SourceCache" /XF "*.tmp" /XJ /L /LOG:"C:LogsRobocopy-preview.log"Check that each exclusion matches what you intend. Excluded files are not copied or updated, and excluded directories are not mirrored. If the destination contains an old excluded copy, do not assume a later mirror will remove or refresh it. A broad wildcard such as *.tmp can affect files in every traversed directory, not just one folder.
Control retries and waiting instead of relying on defaults
Robocopy’s documented defaults are a retry count of 1,000,000 and a 30-second wait between retries. Those settings affect how long the command can remain stuck on an unavailable or locked item; they do not make deletion safer.
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Set deliberate limits for unattended jobs or troubleshooting. /R:n sets the retry count, and /W:n sets the wait interval in seconds. For example:
robocopy "C:Source" "D:Backup" /E /R:3 /W:10 /LOG:"C:LogsRobocopy-run.log"This example allows three retries and waits 10 seconds between them. Choose values that fit the reliability of the source and destination; a low retry count can leave transiently unavailable files uncopied, while the defaults can make a failed operation appear to hang for a very long time. Retry settings concern availability and completion, not whether destination-only files are eligible for purge.
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Important path, permission, and security details
Verify direction before execution
The source and destination are positional arguments. Accidentally reversing them can make the wrong tree authoritative and, with /MIR, expose the intended source to deletion. Read the command left to right and compare both paths with the windows you inspected.
Make sure the log location is usable
The account running Robocopy needs permission to read the source, write the destination, and create or append the log. Store the log somewhere that will remain available after the run, and do not place it inside a directory that the mirror is expected to delete or replace. If the log directory does not exist or is not writable, you may lose the record needed to assess the run.
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Microsoft notes a difference involving a destination directory’s security settings: when /E and /PURGE are used with a destination directory, those settings are not overwritten; /MIR with /E and a destination directory overwrites them. If permissions on the destination are managed separately, account for this behavior before choosing a mirror command. Treat security settings as part of the change review, not just file content.
Be cautious at a volume root
Microsoft documents a historical edge case in which /MIR or /PURGE at a volume root affected System Volume Information. Current behavior skips that named top-level item. This does not remove the need to verify paths: mirroring a volume root has a much wider scope than mirroring a specific project or backup directory.
What to do when destination files must never be deleted
If the destination is an archive, a staging area shared by several users, or a folder where files are added independently, do not use /MIR merely because you want recursive copying. Start with:
robocopy "C:Source" "D:Archive" /E /L /LOG:"C:LogsRobocopy-preview.log"Review the preview, then remove /L for the approved run. Add /XX when you want Robocopy to explicitly exclude destination-only extras from deletion:
robocopy "C:Source" "D:Archive" /E /XX /L /LOG:"C:LogsRobocopy-preview.log"The extra switch documents your intention, but it does not create version history, undo a prior deletion, or protect against a mistaken source path. A separate destination, such as another physical drive, can be part of a backup design, but no destination is safe from a command aimed at the wrong path. If you need recoverable historical versions, use a backup system that retains versions rather than relying on a mirror.
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Troubleshooting a surprising preview or result
- Unexpected deletions are listed: Stop before removing
/L. Recheck the source path, inspect every listed extra, and switch from/MIRto/E(with/XXif appropriate) when those extras must remain. - Nothing appears to copy: Confirm that the source contains the expected files, that the destination is the intended one, and that the preview is not showing an already synchronized tree. Check the log and return code.
- Files are missing from the operation: Inspect
/XD,/XF, and/XJarguments. A pattern or path can exclude more content than intended. - The command takes an extremely long time: Review
/Rand/W. The documented defaults can cause repeated retries with long waits when a file or destination is unavailable. - The return code is 8 or higher: Open the log, identify failed paths, and correct permissions, connectivity, locks, or storage errors before treating the mirror as complete.
- Destination permissions changed: Revisit the distinction between
/E /PURGEand/MIRdescribed in Microsoft’s command reference, and test security requirements with a preview and a controlled directory. - A junction causes unexpected traversal: Add
/XJif linked directory locations should not be followed, then preview again to confirm the reduced scope.
A final preflight checklist
- The source path is the authoritative tree.
- The destination path is correct and writable.
- Any destination-only files that must remain have been identified.
- The command has been run with
/L. - The preview and log show no unintended deletions.
- Exclusions are deliberate and correctly spelled.
- Retry and wait values are suitable for the job.
- The real run retains
/LOG:or/LOG+:. - The return code and log will be reviewed after completion.
The safe way to mirror with Robocopy is not to find a special “undeletable” form of /MIR; it is to verify the direction, preview the exact changes, choose /E when destination extras must survive, and treat the log and return code as part of the operation.
Frequently Asked Questions
How do I mirror folders with Robocopy without deleting files?
Do not use /MIR when destination-only files must survive. Use /E for recursive copying, add /XX when you want extras explicitly excluded from deletion, preview with /L, and review the log before the real run.
Does Robocopy /MIR delete files?
Yes. Microsoft defines /MIR as /E plus /PURGE. Destination files and directories absent from the source can be deleted during a real run.
How can I preview a Robocopy command before it runs?
Add /L. For example: robocopy "C:Source" "D:Backup" /MIR /L /LOG:"C:LogsRobocopy-preview.log". List-only mode does not copy, delete, or timestamp files.
Is /E safer than /MIR for an archive?
For retaining destination-only content, yes. /E copies subdirectories, including empty ones, without itself invoking purge. Preview it and use /XX when appropriate.
What does /XX do?
It excludes destination-only extra files and directories from deletion. The result is not an exact mirror because content absent from the source can remain at the destination.
Should I remove /L after checking the preview?
Only after confirming the source, destination, exclusions, and every planned deletion. Keep the log switch for the real run and review the resulting return code.
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What do Robocopy return codes 8 and above mean?
They indicate that at least one failure occurred. Read the log, identify the affected paths, and correct permission, connectivity, locking, or storage problems before treating the operation as complete.
Can Robocopy mirroring protect older file versions?
No. A mirror reflects the current source tree and can remove destination copies of files deleted from the source. Use a versioned backup design if historical recovery is required.
The Bottom Line
Never treat /MIR as a deletion-free backup switch. Verify the source and destination, preview the exact command with /L, inspect the log for destination-only items, and use /E (optionally /XX) when those items must remain. Keep a log, review the return code, and remember that a mirror preserves the current tree—not older versions.
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