memoryStream.WriteTo(fileStream);

fileStream.CopyTo(memoryStream);
memoryStream.CopyTo(fileStream);

using (FileStream file = new FileStream("file.bin", FileMode.Create, System.IO.FileAccess.Write)) {
   byte[] bytes = new byte[ms.Length];
   ms.Read(bytes, 0, (int)ms.Length);
   file.Write(bytes, 0, bytes.Length);
   ms.Close();
}

using (MemoryStream ms = new MemoryStream())
using (FileStream file = new FileStream("file.bin", FileMode.Open, FileAccess.Read)) {
   byte[] bytes = new byte[file.Length];
   file.Read(bytes, 0, (int)file.Length);
   ms.Write(bytes, 0, (int)file.Length);
}

using (FileStream file = new FileStream("file.bin", FileMode.Create, FileAccess.Write)) {
    memoryStream.WriteTo(file);
}

using (FileStream file = new FileStream("file.bin", FileMode.Open, FileAccess.Read)) {
    byte[] bytes = new byte[file.Length];
    file.Read(bytes, 0, (int)file.Length);
    ms.Write(bytes, 0, (int)file.Length);
}

MemoryStream ms = new MemoryStream(bytes, writable: false);

byte[] testData = new byte[] { 104, 105, 121, 97 };
var ms = new MemoryStream(testData, 0, 4, false, true);
Assert.AreSame(testData, ms.GetBuffer());

MemoryStream ms = new MemoryStream();
FileStream file = new FileStream("file.bin", FileMode.Create, FileAccess.Write);
ms.WriteTo(file);
file.Close();
ms.Close();

MemoryStream ms = new MemoryStream();
using (FileStream fs = File.OpenRead(file))
{
    fs.CopyTo(ms);
}