Looks like I have to search for another solution. Either OS X screw up or the problem within the external HDD. I've tried with my friend NTFS formatted HDD, it read fine. But my own HDD still messed up.
Then I tried using repair disk as suggestion. But this result made more and more confused.
First I verify. Of course this is the result.
http://img703.imageshack.us/img703/5840/img2022v.jpg
Then I try to repair. Disk Utility says it could not unmount the disk but actually I suspect the disk is ejected itself, again. I try to close and re-open disk utility, as I feared… it not detected again.
http://img254.imageshack.us/img254/8022/img2023b.jpg
Trying for the second time, still didn't unmount. This is ridiculous. When one of my partition doesn't mount, the other partition that I want to repair couldn't unmount
http://img822.imageshack.us/img822/4900/img2024b.jpg
I try again, this time I select entire volume, and verify first. Looks like it ejected itself when in the middle of the process
http://img153.imageshack.us/img153/4223/img2025l.jpg
So I noted this is either OS X misbehaving or the underlying problem is my HDD.
I also run another test with AJA benchmark for HDD write/read speed. Fortunately the test is done before the disk ejected again. I think I know why it have longer time for detecting and mount. But still one of partition didn't mount. Of course this is definitely not normal. Write/read speed actually could reach ~50 MB/s.
http://img541.imageshack.us/img541/9700/screenshot20110221at054.png
I could access one of my partition but looking back at that write/read speed, right now I don't want to mess anything.
http://img25.imageshack.us/img25/9700/screenshot20110221at054.png
What I'm planning for the next solution is using either one of this tool: DiskWarrior, Drive Genius, or TechTool Pro. But with my time schedule probably I will do it Tomorrow.