u/gaccha_antiquechair

Old friend of mine gave me her failed HDD (ST500DM002-1BD142, FW:KC45), as usual irreplaceable personal data and no backup. Drive would spin up, seek and initialize but would never get detected by the SATA HBA on any of my systems. Eventually concluded that it was some form of controller failure (I'm not an expert in data recovery, I can recover accidentally deleted / overwritten files, but serious mechanical / electronic stuff is unfortunately out of my league at present), drive was set aside in my junk drive box and left for some months.

Had one of my own old drives fail in a similar manner and got curious, decided to start probing the control PCBs on these failed drives with my scope to see if I could locate some sort of serial data stream or UART interface to interrogate the controller as these PCBs are more or less undocumented black boxes as far as I can tell with information currently available.

Probing with scope didn't turn up much, but did notice that the behavior of this particular drive changed slightly after my poking with the scope probe, seeking period after spin up was longer than before. Decided to give the drive a go and hooked it up, after a longer than normal delay I saw in my kernel logs that the links for the SATA port is now up and the system has enumerated a new block device. Fdisk shows a valid partition structure on the disk, smartctl output is nonsensical, drive parameters are correct but attributes like 'Head_Flying_Hours' 'LBAs_Read/Write' are at zero, definitely wrong for this drive.

Immediately start ddrescue attempt onto recovery media. Read rate is incredibly slow but no errors are being logged. Can see high 'Raw_Read_Error_Rate' and 'Hardware_ECC_Recovered' but no 'Offline_Uncorrectable' errors. To me this says that the drive is struggling to read but the ECC is able to resolve the errors. Eventually do start to see pending sectors increasing and uncorrectable errors, though subsequent passes do seem to succeed. I have logged the smart data periodically over the course of the recovery. can paste-bin if anybody interested.

Six days later and I finally have an image I can mount and try to repair, fsck of returns clean, mount read only, file system appears intact with good data, great success. Returned on new disk to friend who was delighted.

Decided additional investigation was required, power cycled drive, enumerates as block device but with totally wrong parameters nonsense model and serial number, capacity 4.5 Gb?. Took the PCB off again and noticed that the pads that connect the head stack and actuator to the PCB appear badly oxidized, cleaned with Deoxit and fiberglass pencil. Reconnect drive and is enumerated immediately like a good drive. Decide to do a zero fill using dd, completed without error at a speed I would consider normal for this drive. Created new file system and transferred some large files onto it, calculated and compared check-sums which match the originals. Drive appears sane now? Smartctl output did not reset shows original errors no new ones. (Obviously, drive is stuffed and little more than a test subject at this point)

Ultimately I would like to know more about the inner workings of these drives but much of the information on them appears to be insider knowledge / trade secrets. If anybody has advice on some good resources I could study that would be most welcome.

Sorry for long post, success in a scenario like this was genuinely unprecedented for me, just wondering what the pros have to say.

Regards