I'll leave you to solve the mystery of ประเทศไทย on your own (Google, as ever, is your... )... 😉
However, for the sake of completeness (and learning), and since we're in one of those all-too rare but nevertheless heart-warming 'caring and sharing' moments on ASC, I'd like to point out that there's a third way of tackling this problem. So far we have:
1. Don't mount the disk at all (see Leroy's link to Topher's article, marked as the Answer to the thread).
2. Unmount the disk automatically (as we've discovered together; don't forget to save the script as an .app and add to your login items)
3. Leave the disk mounted but have it power down if not in use.
The third option may be more suitable for some, particularly laptop users. After all, once the disk is powered down, it's not affecting system resources even though mounted.
By default, on battery power OS X powers down any disk after 10 minutes of inactivity. You can reduce this default time by manipulating the pmset power management settings in Terminal.
In Terminal.app, copy/paste this command:
sudo pmset -b disksleep 5
After pressing 'return' on your keyboard, you will need to enter an Admin password, which will be invisible when you type it (so type carefully!).
This tells OS X to power down any disk that has not been accessed for 5 minutes (if you want to change it back to the default setting use the same command and replace '5' with '10').
Note that this setting also applies to your startup disk, but since your startup disk is in more or less constant use, it's unlikely to be affected. However, the good thing about this command is OS X will immediately and automatically power the disk back up as soon as you do anything that calls a file on the disk (i.e., you don't have to do anything to get it to power up, OS X will handle it without your intervention).
Personally, I have this set to 5 minutes for my startup disk (I don't have a secondary internal) simply because my battery is 69% health and well past the stage it needs servicing. Having the disk power down after 5 instead of 10 minutes eeks out a bit of extra battery time when I'm not connected to the mains.
You can of course set the disksleep time to less than 5 minutes, but you probably don't want to for two reasons. One, because it affects all connected disks. And two because powering the disk up repeatedly after every, say, 2 minutes (say you're reading something on the net) will likely use more power over all than leaving the disk on. 5 minutes is a useful compromise, but it depends on the user. For your secondary disk, if you're not using it at all, it'll stay powered off after 5 minutes (but still mounted and available) until or unless you access it or call a file that resides on it.