Seagate Momentus 5400.6 becomes ghost after ~10 seconds

Hello,

Observing strange behaviour with a Seagate Momentus 5400.6, Model ST9500325AS, with firmware 0002BSM1 ...

The drive is 500 GB, of which 470 GB could be cloned.

The drive has defective sectors, mostly located in the first 30 GB.

When cloning the untried blocks in those first 30 GB, the speed is not so bad during 5 to 10 seconds, around 9'000 Kb/s to 15'000 Kb/s.

Then the speed displayed becomes frozen and ddrescue cannot be interrupted with Ctrl+C as usual, even if waiting 30 seconds. When opening a new terminal, the drive drive doesn't answer to "fdisk -l".

If I shut down the drive, ddrescue stops instantly.
When I power the drive on, it is detected again.

I observed the problem was worse when the dock was connected in eSATA as the drives becomes faster unvisible. In USB 2, things go a little better, but I still have to power down and on the drive on a very regular basis.

It's like if the drive became temporily busy after about 5 to 10 seconds.
I wonder if the fimware has some bug making the drive lazy as soon as defective sectors is met or if this could come from a weak component, like a capacitor.

It's not a problem of slow cloning ; it's really like a freeze.

Have some of you already seen such drives?