📎 AI Summary:
The thread centers on why a Windows 11 user’s `robocopy` transfer of an eM Client folder to an external drive is fast the first time but takes ~7 hours on the second run, despite expecting duplicates to be skipped. The main guidance is that `robocopy` will skip identical files, so a long second run usually indicates slow scanning/comparison (often due to the USB flash drive’s poor performance or timestamp/attribute mismatches), and contributors recommend using options like `/FFT` plus reducing verbose output, then running a `/L` (list-only) dry run to check the log’s summary for “Copied vs Skipped.” Overall sentiment is troubleshooting-focused and optimistic, with agreement that the storage medium and/or filesystem/timestamp differences are likely the culprit.
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oldgreyguy

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Have an issue with Robocopy, thought you boys & girls might give your opinion/observations on how to resolve this.

1/ Windows 11 computer running EM Client (c:\

2/ RoboCopy Command -- robocopy "C:\users\curtis\documents\em client" "E:\Email" /E /DCOPY:DAT /R:3 /W:5 /V

3/ Em Client folder = 51.1 gb

4/ first time running, took about an hour (1TB flash deive , formatted NTFS)

5/ second run, 30 mins later, took somewhere about 7 hours...Arrgh

assumptions... the above command should have skipped duplicate files (EM Client was not opened between the two runs

Help me mr. wizard(s)
 

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WindowsForum AI
Hi oldgreyguy — your assumption is basically correct: Robocopy should skip files that are identical by name, size, and timestamp. A second run taking 7 hours usually means one of these is happening:

Most likely causes​

  • It is not recopying everything, but it is slowly scanning/comparing everything
  • Robocopy still has to walk the whole source and destination tree.
  • If the eM Client folder contains many small files, a USB flash drive can be painfully slow at metadata reads.
  • The flash drive is the bottleneck
  • Many 1 TB USB flash drives have terrible sustained write/read performance.
  • Some also slow down badly after the first large write because their cache fills.
  • Timestamps are...
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WindowsForum AI

WindowsForum AI

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#2
Hi oldgreyguy — your assumption is basically correct: Robocopy should skip files that are identical by name, size, and timestamp. A second run taking 7 hours usually means one of these is happening:

Most likely causes​

  • It is not recopying everything, but it is slowly scanning/comparing everything
  • Robocopy still has to walk the whole source and destination tree.
  • If the eM Client folder contains many small files, a USB flash drive can be painfully slow at metadata reads.
  • The flash drive is the bottleneck
  • Many 1 TB USB flash drives have terrible sustained write/read performance.
  • Some also slow down badly after the first large write because their cache fills.
  • Timestamps are not matching exactly
  • Even on NTFS, removable drives/controllers sometimes cause timestamp precision weirdness.
  • Add /FFT to allow a 2-second timestamp tolerance.
  • /V is making the run much slower
  • /V creates verbose output for skipped files too.
  • Console output is surprisingly expensive when there are many files.
  • Something is touching the eM Client files
  • eM Client may not be open, but Windows Search, antivirus, backup software, or sync tools may still touch files.
  • If timestamps or attributes change, Robocopy may think files are different.

First thing I would try​

Run this version instead:
robocopy "C:\Users\curtis\Documents\em client" "E:\Email" /E /COPY:DAT /DCOPY:DAT /R:3 /W:5 /FFT /XJ /MT:8 /NP /NFL /NDL /LOG:"%USERPROFILE%\Desktop\emclient-robocopy.log"

What changed​

  • /COPY:DAT explicitly copies data, attributes, timestamps.
  • /FFT relaxes timestamp comparison.
  • /XJ avoids junction-point weirdness.
  • /MT:8 uses 8 threads.
  • /NP removes percentage progress output.
  • /NFL /NDL suppresses file/folder listing.
  • /LOG: saves the useful summary without flooding the console.

To find out whether it is really recopying files​

Do a test-only dry run:
robocopy "C:\Users\curtis\Documents\em client" "E:\Email" /E /COPY:DAT /DCOPY:DAT /R:3 /W:5 /FFT /XJ /L /V /TS /FP /LOG:"%USERPROFILE%\Desktop\emclient-dryrun.log"

Important​

/L means list only. It will not copy, delete, or change anything.
After it finishes, check the summary at the bottom of the log. Look especially at:
Code: 
Files :        Total    Copied   Skipped  Mismatch    FAILED    Extras
Bytes :        Total    Copied   Skipped  Mismatch    FAILED    Extras
If Copied is near zero, Robocopy is skipping correctly and the delay is mostly scanning/logging/USB speed.
If Copied is large, then timestamps/attributes/content are changing.

If you want the destination to be an exact backup mirror​

You can use /MIR, but be careful:
Warning: /MIR deletes files from E:\Email that no longer exist in the source.
Test first:
robocopy "C:\Users\curtis\Documents\em client" "E:\Email" /MIR /COPY:DAT /DCOPY:DAT /R:3 /W:5 /FFT /XJ /MT:8 /NP /L
If the preview looks safe, remove /L:
robocopy "C:\Users\curtis\Documents\em client" "E:\Email" /MIR /COPY:DAT /DCOPY:DAT /R:3 /W:5 /FFT /XJ /MT:8 /NP /NFL /NDL /LOG:"%USERPROFILE%\Desktop\emclient-mirror.log"

My practical recommendation​

For this job, I would use:
robocopy "C:\Users\curtis\Documents\em client" "E:\Email" /E /COPY:DAT /DCOPY:DAT /R:3 /W:5 /FFT /XJ /MT:8 /NP /NFL /NDL /LOG+:"%USERPROFILE%\Desktop\emclient-backup.log"
If the second run still takes hours, I would strongly suspect the USB flash drive, especially if the log shows most files were skipped.
A proper external SSD will likely make this job dramatically faster than a 1 TB thumb drive.

One question​

Can you post the Robocopy summary section from the bottom of the second run? That will tell us immediately whether it spent 7 hours copying or just scanning/comparing.
 

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