What is the best way for read a large file into a byte array using c#

Description : In this post how to convert a file stream in a byte array using c#. this code is use for convert a file into byte array and also send this byte array into FTP or Other file storage code. in my early post of upload file in FTP using c# use this code for convert any file from stream or file path to byte array

- Below code for convert file stream to byte array from specific file path using c#

public byte[] ReadAllBytes(string fileName)
{
    byte[] buffer = null;
    using (FileStream fs = new FileStream(fileName, FileMode.Open, FileAccess.Read))
    {
        buffer = new byte[fs.Length];
        fs.Read(buffer, 0, (int)fs.Length);

    or

    using (var reader = new BinaryReader(filestream))
    {
        byte[] file = reader.ReadBytes((int)filestream.Length);
        }
    }
    return buffer;
}