how to send a large file to Request Stream in asp .net

Question

I want to send large files >800 mb to cassansdra storage.But I am getting System.OutOfMemoryException .

Please find the code below:

HttpWebRequest request = WebRequest.Create(postUrl) as HttpWebRequest;

Stream requestStream = request.GetRequestStream();

byte[] buffer = new byte[8 * 1024];

int len;
while ((len = fileToUpload.File.Read(buffer, 0, buffer.Length)) >0)
{
    requestStream.Write(buffer, 0, len);
    requestStream.Flush();
}
return request.GetResponse() as HttpWebResponse;

Please suggest me which part of the code needs improvement?

fileToUpload is the exact stream of 800 MB from UI.