Robocopy /IPG faster than expected....

[weird_dave]

I wanted to transfer a few files over a vpn which is shared, so I figured I'd use robocopy to limit the bandwidth used, I figured an IPG of 10,000 would at best allow 1 packet of 64KBytes every 10 seconds:

E:\I>robocopy e:\I n:\Library /IPG:10000

-------------------------------------------------------------------------------
   ROBOCOPY     ::     Robust File Copy for Windows
-------------------------------------------------------------------------------

  Started : 15 July 2020 14:20:19
   Source : e:\I\
     Dest : n:\Library\

    Files : *.*

  Options : *.* /DCOPY:DA /COPY:DAT /IPG:10000 /R:1000000 /W:30

------------------------------------------------------------------------------
___ File info Cut ___
------------------------------------------------------------------------------

               Total    Copied   Skipped  Mismatch    FAILED    Extras
    Dirs :         1         0         1         0         0        75
   Files :         8         8         0         0         0         2
   Bytes :   9.640 g   9.640 g         0         0         0    77.9 k
   Times :  43:46:14  43:46:12                       0:00:00   0:00:01


   Speed :               65689 Bytes/sec.
   Speed :               3.758 MegaBytes/min.
   Ended : 17 July 2020 10:06:33

This did not have the desired effect at all, it was more than 10x the expected speed! Kinda glad in a way as 2 days is long enough, but I'd like to understand why it was so much faster.
Anyone experienced this or have thoughts on how it may have happened?

 

[Donnie Fisher]

Are any of the files you are copying already existing on the destination?

IIRC, robocopy by default will skip copying matches that are already there.

If it is skipping, that would explain the faster rate. ... I.e it'll count the file as transferred data adding it to the total even though it had skipped actually moving the data.

Edit.... Sorry just seen the report saying no skips !