using System.Runtime.InteropServices;
...
[DllImport("kernel32.dll")]
private static extern long GetVolumeInformation(
    string PathName, 
    StringBuilder VolumeNameBuffer, 
    UInt32 VolumeNameSize, 
    ref UInt32 VolumeSerialNumber, 
    ref UInt32 MaximumComponentLength, 
    ref UInt32 FileSystemFlags, 
    StringBuilder FileSystemNameBuffer, 
    UInt32 FileSystemNameSize);

private void btnGetInformation_Click(object sender, EventArgs e)
{
    string drive_letter = txtDisk.Text;
    drive_letter = drive_letter.Substring(0, 1) + ":\\";

    uint serial_number = 0;
    uint max_component_length = 0;
    StringBuilder sb_volume_name = new StringBuilder(256);
    UInt32 file_system_flags = new UInt32();
    StringBuilder sb_file_system_name = new StringBuilder(256);

    if (GetVolumeInformation(drive_letter, sb_volume_name,
        (UInt32)sb_volume_name.Capacity, ref serial_number,
        ref max_component_length, ref file_system_flags,
        sb_file_system_name, (UInt32)sb_file_system_name.Capacity) == 0)
    {
        MessageBox.Show(
            "Error getting volume information.", 
            "Error", MessageBoxButtons.OK, 
            MessageBoxIcon.Exclamation);
    } else {
        lblVolumeName.Text = sb_volume_name.ToString();
        lblSerialNumber.Text = serial_number.ToString();
        lblMaxComponentLength.Text = max_component_length.ToString();
        lblFileSystem.Text = sb_file_system_name.ToString();
        lblFlags.Text = "&&H" + file_system_flags.ToString("x");
    }
}