Format command runs slow on Windows2012 when run through service

Question

We have a windows service which performs some tasks. One of such task is format the given volume(volume name is passed from remote machine). We observed that till Windows2008 format was running properly. on Windows2012 same format starts correctly but runs
very slow. One special case if if the format is quick it runs fast (same speed as windows2008).
Another observation is when we start format as process though we set the priority high after start the priority of the process goes to normal
Any reason why format runs slow?
Any help/comments are welcome

Answer 1

here is some code 
We do not use bat file but use process.
Here is some part of code for this
ProcessStartInfo FormatInfo = new ProcessStartInfo();
                FormatInfo.CreateNoWindow = true;
                FormatInfo.UseShellExecute = false;
 FormatInfo.RedirectStandardOutput = true;
                FormatInfo.RedirectStandardInput = true;
                FormatInfo.FileName = "cmd.exe";                
                Process format_process = new Process();
                format_process.StartInfo = FormatInfo;
                if (true != format_process.Start())
                    int errCode = Marshal.GetLastWin32Error();
                    String ErrMsg = "Cannot start formatting. Error code = " + errCode.ToString();
                    Logger.LogDebug(ErrMsg);
                String FormatCmdLine = "Format ";
                FormatCmdLine += m_driveletter + ":";
                if(quick_format)
                    FormatCmdLine += " " + Constants.QUICK_FORMAT_SWITCH + " ";