CODEWITHSUNDEEP
delphi
megatr0n
megatr0n

Reputation: 362

Quickest way to create a large file and quickest way to remove it

I am trying to make a ntfs disk unwriteable by using up all the empty space. Is there a way I can create a file and set the file size to the max size of disk and then reset it to a less value to make it writeable again? If not what is the fastest way to create a file? I am using delphi. Also the fastest way to remove it will be needed too. Thanks.

Upvotes: 1

Views: 913

Answers (1)

Jerry Dodge
Jerry Dodge

Reputation: 27296

You can create a TFileStream and set its size using its Size property. Something like this...

var
  F: TFileStream;
begin
  F:= TFileStream.Create('C:\BigFile', fmCreate);
  try
    F.Size:= 50000000000;
  finally
    F.Free;
  end;

This would create a file C:\BigFile with a size of about 46GB.

You would still have to calculate how big of a file to create based on the amount of free space. Keep in mind that this doesn't actually write any data, it only instructs the file system that the file is a certain size.

To delete the file, just do the same only set the size to 0...

var
  F: TFileStream;
begin
  F:= TFileStream.Create('C:\BigFile', fmCreate);
  try
    F.Size:= 0;
  finally
    F.Free;
  end;
  DeleteFile('C:\BigFile');

EDIT

During my test of large files, I realized that you have to use Int64 instead of Integer in order to accommodate for these large sizes.

Also bear in mind that there are files constantly changing, especially on the Windows system drive. Even two sequential calls to DiskFree and TFileStream.Size could result in an error of not enough disk space available. I'd suggest to write a file for example 100MB less than the free space, then add 1MB at a time until it fails, then add 1KB at a time until it fails, then add 1 byte at a time until it fails. Then you'll know you can guarantee that all space is taken without just raising a single error and completely failing.

This would begin with something like this...

var
  F: TFileStream;
begin
  F:= TFileStream.Create(FILENAME, fmCreate);
  try
    F.Size:= DiskFree(3) - (1024 * 1024 * 100);
    while 1 = 1 do begin
      try
        F.Size:= F.Size + (1024 * 1024);
      except
        Break;
      end;
    end;
    while 1 = 1 do begin
      try
        F.Size:= F.Size + 1024;
      except
        Break;
      end;
    end;
    while 1 = 1 do begin
      try
        F.Size:= F.Size + 1;
      except
        Break;
      end;
    end;
  finally
    F.Free;
  end;

Note this could be constructed better (as far as error handling), but this should give you a good start.

Upvotes: 2

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