bug#69535: Problem with copying an EXTREMELY large file - cmp finds a mismatch

[Paul Eggert]

Try running 'strace -o tr cp data.dat original' and then look at the 
file 'tr' (which could be quite large). Look for the syscalls near the 
start, and near the end, of the bulk copy.

Quite possibly it's a bug in your Linux drivers or your firmware or 
hardware. For example, if you're using ZFS, see:

https://github.com/openzfs/zfs/issues/15526

The strace output might help figure this out.