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Yes. Robocopy can resume an interrupted file transfer when you run it with /Z (restartable mode) or /ZB (restartable mode with a backup-mode fallback). On an interrupted file, Robocopy can continue from its saved checkpoint instead of copying the entire file again. The switch must be present in the original run and in the recovery run; an ordinary rerun without it is not a documented guarantee of checkpoint resume.
What makes Robocopy resume a file?
The relevant option is /Z. Microsoft’s Robocopy command reference describes restartable mode as allowing an interrupted copy to pick up where it stopped rather than recopying the whole file. This applies to the file that was being transferred when the interruption occurred; it does not mean every possible disk, cable, filesystem or hardware failure is automatically recoverable.
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/ZB includes restartable behavior and adds a fallback: if normal access is denied, Robocopy attempts backup mode. Backup mode uses a different access path and is subject to Windows privileges and the permissions on the source and destination. It is not simply a faster spelling of /Z.
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| Command choice | What it does | When it fits |
|---|---|---|
/Z |
Uses restartable mode so an interrupted file can continue from a checkpoint. | Use when restartability matters, especially across an unreliable network, and the normal security context can read the data. |
/ZB |
Starts in restartable mode and switches to backup mode if access is denied. | Use when restartability is needed and backup-mode access is permitted and appropriate. |
| Neither switch | The documentation does not promise checkpoint continuation. | A rerun may skip files that already compare correctly, but do not describe it as guaranteed resume of a partial file. |
For a directory tree, a bounded, logged command could look like this:
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robocopy "C:Source" "D:Destination" /E /Z /R:2 /W:5 /LOG+:"C:Logscopy.log"/E includes subdirectories, including empty ones. The restart behavior comes from /Z; the retry and logging switches solve different problems.
Restarting a copy after Windows or a network interruption
- Stop and identify the original scope. Note the exact source, destination, file-selection switches and restartable option. Do not casually change filters or the destination while recovering.
- Run the same command again. Keep
/Zor/ZBin the command. Robocopy compares the existing destination data and uses restart information when the interrupted file is eligible for continuation. - Bound the retries for the situation. Add explicit values such as
/R:2 /W:5if an unattended job should make two retries with five seconds between attempts. These values are an example, not a universal prescription. - Append to a log.
/LOG+:"C:Logscopy.log"keeps the prior run and the recovery run in one file. Plain/LOG:<file>overwrites the specified log. - Allow the run to finish, then inspect both the summary and exit code. A command that returns control without an obvious console error still needs verification.
Using a saved Robocopy job
If the original operation was saved as a job, preserve that configuration instead of reconstructing it from memory. Microsoft documents /SAVE:<jobname> for writing a job and /JOB:<jobname> for running one. For example:
robocopy "C:Source" "D:Destination" /E /Z /R:2 /W:5 /LOG+:"C:Logscopy.log" /SAVE:NightlyCopyLater, invoke the saved job with the same source and destination context expected by that job:
robocopy /JOB:NightlyCopyCheck the job’s options before recovery. If the saved configuration did not contain /Z or /ZB, adding restartability for the next run does not retroactively create a checkpoint for the earlier run. Keep the original selection rules so the recovery does not silently copy a different set of files.
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Do not confuse resume with retries
/R and /W govern what Robocopy does after a failed attempt: /R:<n> sets the retry count and /W:<n> sets the wait in seconds. They do not make a transfer restartable. A command can retry the same failed operation without being able to continue a partially transferred file.
Microsoft lists unusually large defaults in the command reference: /R defaults to 1,000,000 retries and /W defaults to a 30-second wait. Those are documentation defaults, not sensible settings for every interactive or scheduled copy. An explicit, bounded policy prevents a failed network share from holding a job for days.
| Need | Option | Effect |
|---|---|---|
| Continue an interrupted file | /Z or /ZB |
Enables restartable mode. |
| Try a failed operation again | /R:<n> |
Sets how many retries occur. |
| Control the delay between attempts | /W:<n> |
Sets the wait in seconds. |
| Keep evidence of what happened | /LOG:<file> or /LOG+:<file> |
Creates or appends to a log. |
What happens with permissions and /ZB?
/ZB first attempts normal restartable access. If Windows reports access denied, Robocopy switches to backup mode. That fallback may require an elevated Command Prompt or PowerShell session and appropriate backup privileges; elevation alone cannot overcome an unavailable drive, a disconnected share or a destination that denies writes.
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Use /ZB only when the backup-mode access path is acceptable for your environment. It changes how security is evaluated, so confirm that the account, local policy, share permissions and destination filesystem all allow the operation. If ordinary access works, /Z is the simpler choice.
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How to verify that the resumed copy really succeeded
Read the final Robocopy summary and inspect the log. Microsoft documents a return value of 8 or greater as meaning that at least one failure occurred. Treat that as a failed or incomplete job that needs investigation.
Return values below 8 are status combinations, not a single “perfect” result. They can indicate copied files, extra files at the destination, mismatches, or combinations of those conditions. A nonzero code below 8 therefore does not automatically mean the copy failed, but it does mean you should read the summary and decide whether the extra files or mismatches are acceptable.
| Exit-code range | How to interpret it |
|---|---|
| 0–7 | No Robocopy failure was reported; the individual code describes combinations such as no changes, files copied, extra destination files or mismatches. Review the summary for the exact state. |
| 8 or higher | At least one failure occurred. Check the log for the path, error and retry outcome, then correct the underlying problem and rerun. |
In Microsoft’s Azure migration guidance, Robocopy output can also distinguish data transfer from metadata-only work: “Newer” indicates that file data was copied, while “Modified” indicates that only metadata was updated. That interpretation is provided for the migration scenario, so do not treat the labels as a universal throughput measurement.
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Restartability adds bookkeeping. Microsoft’s Azure migration guidance says /Z adds logging overhead and /ZB adds checkpointing, significantly reducing copy performance. The guidance recommends using these switches cautiously, particularly for unstable network conditions where repeating a large transfer would be more expensive than the overhead.
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For a stable local disk-to-disk copy that can be rerun easily, normal mode may finish faster. For a long transfer over a flaky connection, /Z can reduce the amount of data that must be sent again after an interruption. There is no universal speed winner: the right choice depends on the probability and cost of interruption.
Robocopy also supports multithreaded copying with /MT[:n], accepting 1 to 128 threads and defaulting to 8 when enabled according to Microsoft’s command reference. Threading is a separate tuning decision and does not replace /Z. Test it against the source, destination and network you actually use; do not assume that more threads eliminate restart overhead.
Low free space is a different pause mechanism
/LFSM is sometimes mistaken for another resume switch. It is a low-free-space mode: Robocopy pauses when continuing would push destination free space below a configured floor, then proceeds when space is available. It addresses capacity pressure, not recovery of a partially transmitted file.
Microsoft’s Azure migration guidance describes /LFSM for tiered-storage targets and says it is not supported for a remote SMB share. That guidance also lists incompatibilities with /MT, /EFSRAW and /ZB. If you need both low-space protection and restartability, check the documented constraints for your exact migration scenario rather than combining switches by trial and error.
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Common interruption cases and fixes
The PC restarted while a large file was copying
Rerun the original source and destination with /Z or /ZB still present. Keep the same selection switches and inspect the final log. If the first run did not use restartable mode, Robocopy can still compare completed destination files on a later run, but the documentation does not promise continuation of the partial file.
The network share disconnected
Restore the share and confirm that the path is reachable from the account running Robocopy. Use bounded /R and /W values so the job does not wait indefinitely, then rerun with /Z. A restartable checkpoint cannot help while the source or destination is unavailable.
The rerun reports access denied
Verify both share and NTFS permissions. If policy permits backup-mode access, run an elevated console and use /ZB; otherwise correct the permissions and continue with /Z. Do not assume that /ZB bypasses every security boundary.
The destination contains unexpected files or mismatches
Use the exit code and summary to separate extra destination files from copy failures. Recheck the source, destination and filters before deleting or overwriting anything. Robocopy’s status codes below 8 can legitimately report extras or mismatches without reporting a transfer failure.
Bottom line
Use /Z for documented restartable copying, or /ZB when a backup-mode fallback is both authorized and necessary. Rerun the same job, set deliberate retry limits, append a log, and judge the result from the summary and exit code. Restartability improves recovery from interruptions, but it adds performance overhead and is not a guarantee against every storage or filesystem failure.
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