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Robocopy’s /MIR switch can delete files. It creates a destination tree that matches the source by combining recursive copy with purge behavior, so destination-only files and folders are removed. To mirror safely, verify both paths, preview the exact command with /L, inspect the log, and only then remove /L for the live run. If files at the destination must be retained, use a non-purging copy such as /E instead of /MIR.
What Robocopy “mirror” actually does
Robocopy is the Windows command-line utility for copying directory trees. A mirror is stricter than an ordinary copy: after the operation, the destination is intended to contain the same files and directories as the source. That requires removing destination items that have no counterpart in the source.
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Microsoft documents /MIR 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. Consequently, a command such as robocopy "C:Source" "D:Backup" /MIR can delete an item from D:Backup when that item is absent from C:Source. The deletion is expected mirror behavior, not a Robocopy error.
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Choose the operation that matches your intent
| Switch or combination | What it does | Can it delete destination-only items? | Best use |
|---|---|---|---|
/MIR |
Directory-tree mirror; equivalent to /E and /PURGE. |
Yes. Files and directories absent from the source are purged. | A deliberate exact mirror where the destination may be made identical to the source. |
/PURGE |
Deletes destination files and directories that are missing from the source. | Yes. | Only when removal of destination-only content is intentional. |
/E |
Copies subdirectories, including empty directories, without adding purge behavior. | Not by itself. | Recursive copying or updating while retaining extra destination content. |
/E /XX |
Recursively copies and excludes destination-only extra files and directories from deletion. | No for those excluded extras. | Updating a destination that must keep its own files; the result is not a strict mirror. |
/L |
Lists the planned actions only. Microsoft says files are not copied, deleted, or timestamped in this mode. | No. | Previewing a command before a live run. |
/XD |
Excludes named directories from the operation. | Excluded directories are omitted from the operation; they are not evaluated for copying or purging. | Leaving cache, temporary, or other selected directories out of scope. |
/XF |
Excludes matching files from the operation. | Excluded files are omitted from the operation. | Skipping file types or named files that should not be synchronized. |
/XJ |
Excludes junction points, which Robocopy normally includes by default. | Junctions are left out of the operation. | Avoiding traversal of selected NTFS junctions. |
/XX changes the meaning of “mirror”: destination-only items remain, so the destination can contain more than the source. That is often the right trade-off for a backup or working folder, but it is not an exact replica.
Before you type a command: establish the two paths
- Write down the authoritative source. Decide which folder contains the files you want to preserve. In a normal backup workflow, this is the current working folder; the destination is the backup location.
- Write down the destination separately. Check the drive letter, share name, and every parent folder. A mistyped destination can point the command at a different disk or network share.
- Check that the source is the intended root. Mirroring
C:UsersAlexDocumentsis very different from mirroringC:UsersAlex. Do not remove a parent folder from the path merely to make the command shorter. - Decide what destination-only content means. If the destination contains older versions, manually placed files, or folders from another job that must remain, an exact
/MIRoperation is the wrong choice. Use/E, optionally with/XX, and preview that plan instead. - Confirm access. The account running the command needs to read the source and write the destination. Permissions, locked files, offline network shares, and filesystem rules can cause failures even when the paths are correct.
Do not paste a command from an example and run it unchanged. In particular, never assume that a drive letter shown in a guide refers to the same disk on your computer.
Preview a mirror without copying or deleting
Add /L to the command to obtain a list-only run. The following is a preview template for a mirror:
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robocopy "C:Source" "D:Backup" /MIR /L /LOG:"C:LogsRobocopy-preview.log"With /L present, Robocopy reports what it would copy, what it considers extra at the destination, and what it would remove, but it does not copy files, delete files, or update timestamps. The log path is also an example; make sure the log directory already exists or choose a location that your account can create.
For a non-purging recursive copy, preview this instead:
robocopy "C:Source" "D:Backup" /E /L /LOG:"C:LogsRobocopy-preview.log"Do not describe a preview as a backup. It is a plan, not a second copy of your data and not a rollback mechanism. If the source changes after the preview, the live run can produce a different plan, so perform the preview close to the time of the real operation.
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How to inspect the preview and log
Read the console output and the log from the top down. First confirm that the source and destination roots shown by Robocopy are exactly the two paths you intended. Then inspect each category of change:
- New files and directories: items present in the source that would be added to the destination.
- Changed or mismatched items: files whose size, timestamp, attributes, or other comparison details indicate that the destination would be updated.
- Extra files and directories: items found only in the destination. Under
/MIRor/PURGE, these are candidates for deletion. - Excluded items: files or directories omitted because of
/XD,/XF, or/XJ. Exclusion means Robocopy will not synchronize that content.
Open the log in a text editor and search for the names of any destination-only files you care about. If a single unexpected folder appears as extra, stop and correct the source, destination, or exclusion list before running without /L. A clean-looking summary is not enough; an incorrect root can make every listed action appear internally consistent while still targeting the wrong data.
If destination files must stay, avoid purge behavior
Use /E for a recursive update
/E copies the complete source tree, including empty subdirectories, but it does not itself purge destination-only content. This makes it the safer starting point when the goal is “copy and update” rather than “make identical.” Preview it first with /E /L, then remove only /L after reviewing the output.
Add /XX when extras must be explicitly protected
/XX excludes extra files and directories at the destination from deletion. A template that combines recursive copying, list-only preview, and logging is:
robocopy "C:Source" "D:Backup" /E /XX /L /LOG:"C:LogsRobocopy-preview.log"Use /XX when keeping destination-only items is a requirement, and understand the consequence: the destination will not be a strict mirror. If a destination-only item should be removed, delete it through a separately reviewed process rather than adding /MIR casually to this command.
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There is no switch that makes /MIR an exact mirror while also guaranteeing that destination-only files survive. Purging and retaining extras are opposite policies. Choose one deliberately and record that choice in the job’s notes or script comments.
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Limit the scope with exclusions
Exclusions are useful when a source tree contains content that should not be synchronized, but they can also create gaps that are mistaken for successful backup. Verify every pattern in a list-only run.
/XDfor directories: specify directories such as a cache or temporary workspace that should be outside the operation. An excluded directory and everything under it is omitted./XFfor files: specify file names or patterns that should be skipped. Confirm that the pattern does not also match documents you need./XJfor junctions: use this when you do not want Robocopy to follow junction points. Junctions can make a tree appear to contain locations outside the apparent source root, so decide whether following them is appropriate.
When using exclusions with /MIR, remember that excluded content is not evaluated as part of the mirror. Keep a written list of exclusions and review it whenever the folder layout changes.
Run the live operation only after the plan is approved
- Make a final path check. Compare the source and destination in the command with the roots you approved in the preview log.
- Remove
/Land keep logging enabled. For an intentional mirror, the live template is:
robocopy "C:Source" "D:Backup" /MIR /LOG:"C:LogsRobocopy-run.log"- Use
/LOG+:when appending to an existing log. For example,/LOG+:"C:LogsRobocopy-history.log"preserves earlier entries instead of replacing the file. - Wait for the command to finish. Do not close the console or disconnect a network destination while files are still being processed.
- Read the completed log. Look for failures, skipped items, unexpected extras, and the final summary. A command returning to the prompt does not by itself prove that every file was copied.
- Record the return code. Robocopy communicates the result through its process exit code; interpret it together with the log.
Microsoft recommends logging so that you can review the operation’s integrity after it runs. A log is evidence of what Robocopy attempted and reported; it does not preserve deleted destination files.
Set bounded retries for real-world interruptions
Robocopy’s default retry count is 1,000,000 and its default wait interval is 30 seconds. Those defaults can make a job appear hung when a file is locked or a network share is unavailable. They affect how long Robocopy keeps trying, not whether destination-only files are deleted.
Set deliberate values with /R:n for the number of retries and /W:n for the wait in seconds. For example:
robocopy "C:Source" "D:Backup" /E /XX /R:3 /W:5 /LOG:"C:LogsRobocopy-run.log"This example makes three retries with a five-second wait and retains destination extras through /E /XX. Select values appropriate to the reliability of the local disk or network share. A low retry count can leave transiently unavailable files uncopied; a high count can delay detection of a permanent permission or connectivity problem.
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Interpret Robocopy’s return codes
Robocopy’s exit code is not a simple “zero means success, nonzero means failure” convention. The documented meanings combine copied, extra, and mismatched states. Codes 8 and above indicate that at least one failure occurred.
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|---|---|---|
| 0 | No files were copied, and there was no failure or mismatch. | Confirm that “nothing to copy” was expected. |
| 1 | All files copied successfully. | Review the log for the expected file count and scope. |
| 2 | Extra files or directories exist at the destination. | Decide whether extras are intentional. Do not assume they were deleted. |
| 3 | Files were copied and extra files or directories exist. | Check whether the selected switches were meant to retain extras. |
| 5 | Files were copied and mismatches were detected. | Inspect mismatched entries and the comparison criteria in the log. |
| 6 | Extras and mismatches exist, with no files copied or failure reported. | Review the destination state and determine whether the differences are expected. |
| 7 | Files were copied, with mismatches and extras. | Inspect all three categories before treating the run as complete. |
| 8 or higher | At least one failure occurred. | Read the error lines, correct permissions, paths, locks, or connectivity, then rerun a preview. |
The command’s purpose changes how you judge a lower code. For example, code 2 can be acceptable after an /E /XX update because retaining destination extras is intentional, while the same result may signal an incomplete exact mirror.
Security settings and root-level edge cases
Microsoft documents a security-setting difference between /E with /PURGE and /MIR when the destination directory already exists. With /E and a destination directory, destination directory security settings are not overwritten; /MIR, which combines /E and /PURGE, overwrites those settings. If permissions on the destination are important, review them separately and test the chosen command on a noncritical folder.
Microsoft also notes a volume-root edge case involving System Volume Information. Current behavior skips that named top-level item when /MIR or /PURGE is used at a volume root. This does not remove the need to verify paths: root-level mirroring still has a much wider scope than mirroring a dedicated data folder.
Common failure scenarios and safe fixes
The preview lists files you expected to keep as “extra”
Stop before the live run. Confirm that the source is the authoritative folder. If those files belong only at the destination, change the command to /E, optionally add /XX, and preview again. Do not try to protect them by running /MIR and hoping the deletion list is ignored.
The destination is empty or unexpectedly small
Check the source path, drive letter, and spelling in both the command and the log. A valid but wrong source can produce a valid-looking mirror that removes most of the destination. Correct the paths, run with /L, and inspect the new listing before copying.
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Files remain uncopied after the run
Look for access-denied, locked-file, offline-share, or path errors in the log. Check that the account can read each source item and write the destination. If the problem is transient, use bounded /R: and /W: values and rerun after correcting connectivity or locks. A return code of 8 or higher requires investigation rather than being treated as a successful backup.
An exclusion removed too much from the plan
Review every /XD, /XF, and /XJ pattern. Remove or narrow the matching exclusion, then run another list-only preview. Excluded data is not synchronized, so its absence from the output is not proof that it was safely copied elsewhere.
The log cannot be written
Choose a log directory that exists and is writable, or create it before running Robocopy. Keep the log outside a folder that the mirror could purge, such as a separate logging directory or drive. If the log location is inside the destination tree and you use /MIR, a destination-only log can itself become a purge candidate.
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A mirror is synchronization, not versioned backup. If a file is accidentally deleted from the source and you run /MIR, the corresponding destination file is eligible for deletion during the next run. Keep an independent copy, snapshot, or versioned backup when recovery from accidental source deletion, corruption, or ransomware matters. A separate physical destination drive is one possible arrangement; it is not required for Robocopy and does not by itself make /MIR safe.
For network or cloud-backed destinations, verify that the provider preserves the permissions, timestamps, path lengths, and file semantics your workload needs. Microsoft’s Azure Files migration guidance shows Robocopy being used with that service, but the same preview-and-review discipline still applies: a network destination does not change what /MIR means.
Two complete decision examples
Exact mirror of a disposable staging destination
You want D:StagingMirror to contain exactly the current contents of C:Staging, and anything left only in the destination is disposable.
- Preview with
robocopy "C:Staging" "D:StagingMirror" /MIR /L /LOG:"C:Logsstaging-preview.log". - Verify both roots and review every destination-only item in the output.
- If the deletion list is correct, run
robocopy "C:Staging" "D:StagingMirror" /MIR /LOG:"C:Logsstaging-run.log". - Review the final log and return code, paying particular attention to code 8 or higher.
Update a backup folder that contains manually retained files
You want new and changed files from C:Projects copied to D:BackupProjects, but a manually saved archive in the destination must remain.
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- Preview with
robocopy "C:Projects" "D:BackupProjects" /E /XX /L /LOG:"C:Logsprojects-preview.log". - Confirm that the archive appears as an excluded extra rather than a deletion candidate.
- Run the same command without
/L, retaining/E /XXand the log. - Review the return code and log. The destination will contain the copied project tree plus the retained archive, so it is intentionally not an exact mirror.
Final safety checklist
- The source path is the authoritative folder, and the destination path is the intended target.
- You understand whether destination-only files may be deleted.
- You selected
/MIRonly for an intentional exact mirror; otherwise you selected/E, with/XXwhen extras must remain. - You previewed the exact paths and switches with
/L. - You read the preview and log, including the list of extras and exclusions.
- You removed
/Lonly after approving the planned changes. - You kept
/LOG:or/LOG+:for the live operation. - You chose deliberate
/R:and/W:values when retries could otherwise take a long time. - You reviewed the completed log and interpreted the return code.
- You maintain an independent recovery copy when deletion or corruption would be unacceptable.
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