Thanks, Pepe.
Probably you're right about overheating : all these drives develop a lot of heat because of high rotational speed, electronics and probably design ; the PC chassis should act as a heatsink, but I see everyday HDDs mounted with just 2 screws out of 4 or not well-tightened, or simply not considering adequate venting.
I think that you can't use cheap drives in mission critical systems that run 24/7 just thinking about the price when building up a PC or workstation....
Anyway , investigating some more, I discovered that G-LIST was getting bigger and bigger (obviously, growing defects...) , clearing it didn't change anything
By the way, tried resetting SMART attributes/thresholds/logs and reset the security (password) , but didn't change anything (it was a last resort because problems on these items I know that could lead to extreme slowliness of HDDs...)
Running MHDD SMART short test reported that the test halted at 60% (code 130) with the read element failed (obviously), MHDD scan show a lot of X, A and delays...
How strange ! Almost all the failing drives I have seen had problems on the system area and data area almost intact, this one is the exact opposite !!!
Anyway, keeping cloning is OK but at a rate of 2,000,000 blocks in 2 days , considering the partition has 122,000,000 blocks to be cloned it will take months to get the job done (too much ?!) and I think the drive will break in a few days.
This is one of the situations where data recovery is not worth, maybe. It will take less time typing back the data stored on the drive.
But everything is experience and is worth the time spent testing and trying....
Has anybody experienced something similar and want to share his opinion?
Regards.