In case anyone has issues with RoboCopy and / or XCopy (robocopy replaced xcopy). These utilities are single threaded and pull their resources directly out of the paged pool memory (according to microsoft). Therefore on very large copies these utilities can fail, speaking from recent experience.
I found a workaround which is free or you can pay for the pro version called Taracopy. Not sure what you get with the pro version but using the trial version I was able to move, copy and verify 2TB of data (split across 8 files) successfully. This same grouping of data RoboCopy and XCopy failed to successfully copy.