Random File Generator (again!)

Question

I badly need a random file generator that generates a truly random, non-compressible dummy files.

I ended up with this delphi code. It works, but it's painfully sloooow

 var
    Buf     : Integer;
    TheFile : TFileStream;
 begin
      TheFile := TFileStream.Create(FileName, fmCreate OR fmOpenReadWrite);
      with TheFile do
      begin
           for i := 0 to FileSize do    // Iterate
           begin
                Buf := Random(999999) * i;
                WriteBuffer(Buf, SizeOf(Buf));
           end;    // for
      end;    // with
 end,

My question is: Is there a fast random file generator that I can use? Both Delphi code and/or commandline tools are acceptable as long as:

1. I can run it on Windows without manual intervention (I need this for my tests, no intervention is allowed)
2. It's fast
3. Files generated is non-compressible (ie. compressing the generated file results in no space saving)

---

EDIT For those interested, I applied the advice I received here and made this function, it's fast enough & 7zip has hard time compressing the generated data.

Answer 1

Use a 4096-byte page-size, or multiple page-size, buffer. Writing one integer at a time will be slow.

Answer 2

You can use my generate_random_file.py script (Python 3) that I used to generate test data in a project of mine.

• It works both on Linux and Windows.
• It is very fast, because it uses os.urandom() to generate the random data in chunks of 256 KiB instead of generating and writing each byte separately.