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If a file transfer stops halfway, the destination may contain only an incomplete copy. Keep the original intact, check the source and destination, resume with a tool that supports it, then compare the files’ SHA-256 hashes. A failed transfer alone does not identify the cause: storage, file-system, connection, destination-space, or application problems are all possibilities.
Why a transfer can stop or leave a damaged-looking file
An interrupted copy can leave an incomplete destination file. The cause may be a disconnect, an application or network interruption, too little free space, or a source that was already unreadable. These are possibilities to investigate, not a diagnosis. Microsoft notes that disk, file-system, and storage problems can lead to corruption, inaccessible drives, and failures (Microsoft’s Windows storage troubleshooting guidance).
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Cloud and service-based transfers may have their own behavior. For example, Microsoft’s Azure Files API tracks asynchronous copy status, and an aborted copy leaves a zero-byte destination file; that specific behavior should not be assumed for other services (Azure Files Copy File API).
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What to do before trying the transfer again
- Protect the original. Do not delete it or overwrite a known-good copy. If the source drive is behaving abnormally, stop repeated attempts. Back up important readable files before disk repair or modification; Microsoft recommends a backup before repair (Windows storage troubleshooting guidance).
- Check both ends. Open the original if possible, confirm the destination is connected, and make sure it has enough free space for the file. A loose cable, unreliable port, or disconnect is also worth checking.
- Identify the transfer method. Resume behavior depends on the operating system and app. The commands below apply to Windows; other systems and services have their own resume and verification features.
Resume a Windows transfer with Robocopy
For a folder tree on Windows, Robocopy’s /Z option enables restartable mode. Microsoft says an interrupted file copy can continue where it left off rather than recopying the entire file (Robocopy command reference). Set retry count with /R:n and the wait between retries with /W:n. The following is an example; replace the paths and retry settings to suit your situation:
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robocopy "C:SourceFolder" "E:DestinationFolder" /E /Z /R:2 /W:2 /LOG:"C:copy.log"/E includes subdirectories, including empty ones. The log gives you a record to inspect after the run. Do not treat a progress display alone as proof of success: check the log and Robocopy’s exit code. Microsoft documents exit codes of 8 or higher as indicating that at least one failure occurred; lower codes can still report copied files, extra destination files, or mismatches, so interpret them using the reference’s exit-code table.
Avoid /MIR unless you intend to mirror the source and delete destination items that are absent from it. Microsoft documents that mirror behavior as purging those extra destination items (Robocopy command reference).
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Resume a single-file Windows copy after a connection drop
For a single file when the connection may drop, Microsoft documents copy /Z as resumable after the connection is re-established. The /V option verifies that newly written files were recorded correctly; checking recorded sectors can reduce performance (Windows copy command reference).
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Check whether the destination matches the source
Compare SHA-256 hashes to check whether two files have matching contents. In Windows PowerShell, Get-FileHash uses SHA256 by default. Run it on both paths and compare the Hash values:
Get-FileHash "C:SourceFolderlarge-file.zip" -Algorithm SHA256
Get-FileHash "E:DestinationFolderlarge-file.zip" -Algorithm SHA256If the hashes match, the two files’ contents match. This does not prove the original was uncorrupted before the transfer. If they differ, the files are not identical; copy again to a new destination filename and investigate the source, destination, and connection. Microsoft documents the command and its default algorithm in the Get-FileHash reference.
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When repeated failures point to a storage problem
If the source or destination disconnects repeatedly, errors recur, or the same device fails across ports or computers, stop experimenting on the only copy. Back up what remains readable. On Windows, Microsoft recommends chkdsk /scan to look for potential storage-system issues. Identify the correct volume and protect important data before attempting repair; a repair command is not a guarantee of file recovery (Windows storage troubleshooting guidance).
If a scan reports corruption or important files are at risk, consider qualified data-recovery support rather than continuing experiments with the only copy.
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