I tried the GGW-H20L drive in another computer first, and got it to continue reading missing sectors from an earlier scan of the bad DVD (via other drives) with about 700,000 (!!) missing sectors.
The GGW-H20L did pick up/read some missing sectors but not as fast as I thought or expected. However, that computer started to go to sleep or standby mode every now and then by itself!? I suspected a problem with the GGW-H20L drive, so I installed it in another computer (my main computer).
The GGW-H20L was then set to continue scanning the 86,429 missing sectors from the latest scan by previous drives (primarily the LiteOn iHAS324 C), and appeared to work without issue. After 14 minutes the GGW-H20L failed to read any of the missing sectors. In comparison, the LiteOn iHAS324 C drive I have would probably have successfully read some sectors during that 14 minutes.
I'm using the iHAS324 C drive performance as a benchmark for selecting other drives for reading bad DVD's. The other drives MUST be able to at least read some of the 86,429 missing sectors within 10 minutes, but preferably read quite a few more sectors during the 10 minutes or so. If any drive fails to read any data within that period, then that drive will be rejected (and on-sold).
The other LG drive I have (GH24NSD1) didn't read the missing/bad sectors particularly well either, but, seemed to read a few more than the GGW-H20L on the early scan with 700,000 missing sectors. So the GH24NSD1 drive appears to be a slightly better drive at reading the failing data than the GGW-H20L. But it is only a slight difference, and is not as good as the LiteOn iHAS324 C drive, so the GH24NSD1 drive is also for sale.
The faulty DVD is a commercially pressed one. It was fine initially and played back fine for a couple of years or so. Only recently has this disc begun to play up due to deteriorating media, I believe.
Thanks for the offer of a program to read data off bad discs, but I prefer to use IsoPuzzle as I want to recover as much data as possible without skipping over bad sectors. This is particularly important as the bad area of the disc is right in the middle of one episode of a TV series, and I would like to recover that episode in full, if possible.
IsoPuzzle can be set to re-read bad sectors indefinitely until sectors are successfully read. This is how I've set it up. I've managed to successfully recover data from another bad DVD using IsoPuzzle recently, so IsoPuzzle does work. It is the reading drive that is the determining factor as to how much and how soon data can be recovered.