"diff" terabyte files

You can use bdiff. It is used to compare files that are too large to be loaded in memory.

NAME
     bdiff - big diff

SYNOPSIS
     bdiff filename1 filename2 [n] [-s]

DESCRIPTION
     bdiff is used in a manner analogous to diff  to  find  which
     lines  in  filename1  and filename2 must be changed to bring
     the files into agreement. Its purpose is to allow processing
     of  files too large for diff. If filename1 (filename2) is -,
     the standard input is read.