If you want to use same class then try given code. This is not most optimum memory usage wise but still this should work.
string filename = openFileDialog1.FileName;
var lineCount = 0;
while ((line = reader.ReadLine()) != null)
{
if (GlobalDataClass.dDataArray.GetLength(0) == lineCount)
{
double[,] newTemp = GlobalDataClass.dDataArray;
int increaseLenght = newTemp.Length + 1000;
GlobalDataClass.dDataArray = new double[increaseLenght, 2];
Array.Copy(newTemp, GlobalDataClass.dDataArray, newTemp.LongLength);
}
var data = line.Split(',');
GlobalDataClass.dDataArray[lineCount, 0] = double.Parse(data[0]);
GlobalDataClass.dDataArray[lineCount, 1] = double.Parse(data[1]);
lineCount++;
}