External HDD is corrupted

[compdoc]

> I also ran a full chkdsk scan to check for bad sectors, and it found no
problems.

Chkdsk is getting to be pretty old and although MS has updated it, chkdsk
has very limited use for detecting bad sectors. Mainly because modern drives
'reallocate' bad sectors as they occur, so the OS rarely sees the bad
sectors. 

Unfortunately, reallocation doesn't guarantee your data is not damaged in
the process. Also, when you notice a drive is having problems, I think it's
a bad idea to run extended tests on it, because you're more likely to
further risk your data by working the drive hard.

A hard drives records everything that happens in its lifetime in SMART, so
the best way to know if your drive is failing is to read the SMART info on
the drive. 

You can use the gnome Disk Utility to read SMART, and you want to pay
attention to these values:

Reallocated sector count
Current pending sector count
Reported Uncorrectable Errors (I think this one is more rare)
Temperature

And since the drive is in an external enclosure and subject to getting
knocked around, look at:

GSense Error rate

The actual, important numbers for these events is in the last column, often
named 'Raw'. If you have anything other than all zeros in this column for
the mentioned attributes, the drive is experiencing hardware failures.