Rescuing a HDD - how to handle buffer i/o errors?

[HariboTer]

Hi,
two weeks ago, my desktop PC was running fine, no problems reported / foreshadowing, when suddenly the Windows 7 explorer stopped responding, Task Manager would not appear, the task bar became inactive and pixel fragments appeared on my screen. I kept the hardware button (with which I would normally turn my PC on) pressed, so it shut down a couple of seconds later. Restarting it, trying to launch Win7 in secure mode resulted in a BSOD ("UNMOUNTABLE_BOOT_VOLUME"), system repair did not appear (frozen in loading screen) and the Win7 installation CD (with which I intended to do a recovery of the file system) froze too (inbetween "Windows loading files" and the screen to choose an option). So I inserted the hardware check CD (made&included by the manufacturer of my desktop PC) to check for errors. It ran for quite a while, when on reaching the hard disk drive check, it tested from [] the beginning of the medium - check passed [] the end of the medium - check passed [] random parts of the medium - check passed [] full medium surface - encounters an error after 1-2 hours, stops.
So I concluded my HDD (1 TB internal HDD) would have a few faulty sectors. It took me until the beginning of this week to have a new PC (laptop) setup with a new Win7 and an external HDD drive (the ones where you can/have to insert an internal HDD, with USB 3.0) to access my data from another computer. The HDD was barely recognized, only a 8GB partition of it showed up at first (labeled recovery, ~4GB full, no content shown) and a "F:" medium which I could not access. Trying to get to the filesystem (I was thinking that, except of the faulty sectors, I should get the data I wanted), chkdsk F: /r reached step 2, then suddenly stopped and the external HDD had vanished from any display on my PC, as if I had plugged it out (which I hadn't). Wondering if it had fully passed away, I reconnected it, the same procedure repeated and chkdsk even reached step 4 until it stopped with an error code (interestingly, every percentage shown only went up to 20%).
So I made further research and stumbled upon clonezilla, and as soon as I had aquired a 2 TB external hard drive yesterday evening, I booted my laptop from disk with both hard drives (external and "internal") plugged in via USB 3.0, went to "disk_to_local_disk" etc, leaving every option at default except of -rescue, which I activated. When it started copying, I left and returned 15-30 minutes later to find it chugging around 117 xxx xxx xxx , stating "WARNING: Cant read sector [number], lost data" (with the info "Buffer I/O error on device sbc3, locigal block, [another number]"). A few hours later I went sleeping, this miday I found it to have reached 480 xxx xxx xxx, still stating the same error pattern. So I'm wondering:

• Does it make sense to let it finish?
• In old threads (from around 2011), I read something about gddrescue. Is this by now integrated into clonezilla or can it help on this problem at spots where clonezilla cant? If yes, why?
• Would it be advisable to try a clone from the end of the medium to the start of the medium ("backwards")? (Or in other words, is it likely that there is an "obstacle" that causes any reading attempt that would "go over it" to stop, so if the obstacle is the sign 0 and we have data 1 and 2 positioned like 102, a forwards read can not reach 2 and a backwards read can not reach 1, so both are needed to get the full data?)
• I am running the Clonezilla Live amd64 version on an Intel i5 processor with 2 cores @ 2.9 Ghz (meaning it can sustain up to 4 threads). I do not know how "thread-safe" clonezilla is internally, but the graphics are distributed all over my monitor, meaning I get messages like "C43an 'mitn5 7resad" highlighted by a heterogene mix of colors, and every few seconds it refreshes to show me a new kind of mess^^ The warning/error-message are readable to a point that I can determine their existence and the current number of it, but everything else is a gamble to understand. On the one hand, I'd just like to let you know that there is a problem with that (e.g. the time or percentage display are oblivious to me) and on the other, should I be worried? May it be that the threads block each other when trying to read from the HDD?

Thank you for your assistance in advance! ;-)
With friendly regards,

HariboTer

[Steven Shiau]

Clonezilla is not really a good software for handling physical issue on hard drive, i.e. when you see buffer i/o errors, it's normally physical issue.
It's recommended to use ddrescue, which is also available on Clonezilla live.

Steven.