Copy (backup) from drive a to b "there is not enough space"

Last night I was copying 2.75tb from drive A to B, I let it run all night came back in the morning and it was froze up 99% of the way through the copy. So I scanned B, rebooted and tried to copy the remaining 55gb but I got the error "there is not enough space on B" I have 800gb available on B, and although I had 2.75tb of files selected (from A) my intent was to opt to "skip" all the existing files on B which would have left me with about 16 times as much space as I needed to complete the operation.

Windows is assuming that all the files I am copying are new unique files (2.75tb of them) and I won't be "skipping" 99% of those files I have selected for the operation & because I only have 800gb free I won't have enough space.


Any suggestions how I can get around this problem?

thanks
Robert Christ

Well I kinda solved it, Because I had 800gb free on the target drive I systematically selected small sections of the 2.75tb source drive for copying that were smaller than the 800gb free on the target drive.

I like the feature warning you that the selected files are larger than the target device but apparently Microsoft engineers never considered the problem I came up against that although the files I had selected were larger than the available space on the target device many of them would have been canceled out by the existing identical files already on it.
Robert Christ