function FullDirectoryCopy(SourceDir, TargetDir: string; StopIfNotAllCopied,
    OverWriteFiles: Boolean): Boolean;
var
    SR: TSearchRec;
    I: Integer;
begin
    Result := False;
    SourceDir := IncludeTrailingBackslash(SourceDir);
    TargetDir := IncludeTrailingBackslash(TargetDir);
    if not DirectoryExists(SourceDir) then
      Exit;
    if not ForceDirectories(TargetDir) then
      Exit;

    I := FindFirst(SourceDir + '*', faAnyFile, SR);
    try
      while I = 0 do
      begin
        if (SR.Name <> '') and (SR.Name <> '.') and (SR.Name <> '..') then
        begin
          if SR.Attr = faDirectory then
            Result := FullDirectoryCopy(SourceDir + SR.Name, TargetDir + SR.NAME,
              StopIfNotAllCopied, OverWriteFiles)
          else if not (not OverWriteFiles and FileExists(TargetDir + SR.Name))
            then
            Result := CopyFile(Pchar(SourceDir + SR.Name), Pchar(TargetDir +
              SR.Name), False)
          else
            Result := True;
          if not Result and StopIfNotAllCopied then
            exit;
        end;
        I := FindNext(SR);
      end;
    finally
      SysUtils.FindClose(SR);
    end;
end;

Пример использования:

FullDirectoryCopy('C:\a', 'D:\b');

program Project1;

{$APPTYPE CONSOLE}

uses
    SysUtils;

var
s: String;

begin
s:='qwhqwgdyuqwgydqwbxqwfqwjioqwejfiohxchqwixuwxqjijxhuihqhwnnxqwionxoqijxmxowqadjhduiqwhqwhqwgdyuqwgydqwbxqwfqwjioqwejfiohxchqwi  xuwxqjijxhuihqhwnnxqwionxoqijxmxowqadjhduiqwhqwhqwgdyuqwgydqwbxqwfqwjioqwejfiohxchqwixuwxqjijxhuihqhwnnxqwionxoqijxmxowqadjhduiqwhdsfsdfsdf'  ;

writeln(s);
readln;
end.