try mo magenter sa bios kung na reread.
if readable naman try this command on cmd chkdsk yourExternalDrive: /r
ay readable naman pala try to uninstall the driver then restart and try to optimize
$img_ext=explode(".",$image);
$image_ext=$img_ext['1'];
$image = rand(1,1000).rand(1,1000).time().".".$image_ext;
move_uploaded_file($tmp_image,"../sample/sample_img/$image");
ito idea