I'm using robocopy to copy a large number of files (300,000 files totalling around 4TB) from one NAS drive to another. Here is a sample command:
robocopy \\nas1\myfolder \\nas2\myfolder /E /R:1 /W:5
I've done this hundreds of times before across a wide variety of folders and drives without any issue. In each case, as it finishes copying a file, it always reported 100% before moving on to the next.
However, I'm suddenly getting less-than-100% transfers being reported. Usually 98-99% but sometimes as low as 30%. See image:
The robocopy command is still running (expected to take several hours) so I cannot yet determine the validity of the copied files or do any checks.
In what circumstances would robocopy do this? Is there a problem with the transfer or is it reporting partial progress in threads or something?
Update: Small files (< 1k) tend to be worst affected, reporting < 50% in many cases. Large files (> 10MB) tend to report 98%+