Ant wrote

Ah, so http://www.kalysto.org/utilities/dd_rhelp/index.en.html is
useless then.

Yep, with that utterly obscene number of Offline uncorrectable sectors,
the bulk of those are never going to deliver the data in them again, no
matter how often you retry. It must have had a head crash and there is
lots of debris floating around in the sealed chamber quite apart from
the massive number of sectors gouged right off the platters.

I wonder if that SMART error last year on April 19th was the start of it
or unrelated:

Most likely unrelated. There is no reason why a head crash
and that is almost certainly what has happened to produce
that utterly obscene number of Offline uncorrectable sectors,
would have seen just one turn up well before the head crash.

I guess its theoretically possible the the media has just
started to come off the platters and that is why there
has been a head crash, the initial debris gets repeatedly
jammed under the flying heads and sees massive
amounts of loose debris floating around in the
chamber and it’s the first bit of media coming
off the platter that produced that first offline
uncorrectable sector, but media just coming
off the platter because it was never bonded
to the platter properly is pretty uncommon
with a drive like that.

That early one is much more likely to have been
due to a power flick while the drive was writing.

=== START OF READ SMART DATA SECTION ===
SMART Attributes Data Structure revision number: 10
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED
WHEN_FAILED RAW_VALUE
1 Raw_Read_Error_Rate 0x000f 056 053 006 Pre-fail
- 208576601
3 Spin_Up_Time 0x0003 098 098 000 Pre-fail
- 0
4 Start_Stop_Count 0x0032 100 100 020 Old_age
- 0
5 Reallocated_Sector_Ct 0x0033 100 100 036 Pre-fail
- 6
7 Seek_Error_Rate 0x000f 089 060 030 Pre-fail
- 928963346
9 Power_On_Hours 0x0032 019 019 000 Old_age
- 71036
10 Spin_Retry_Count 0x0013 100 100 097 Pre-fail
- 0
12 Power_Cycle_Count 0x0032 100 100 020 Old_age
- 362
194 Temperature_Celsius 0x0022 038 053 000 Old_age
Always - 38
195 Hardware_ECC_Recovered 0x001a 056 053 000 Old_age
Always - 208576601
197 Current_Pending_Sector 0x0012 100 100 000 Old_age
Always - 1
198 Offline_Uncorrectable 0x0010 100 100 000 Old_age
ne - 1

That's only real indication of a problem at that time.

199 UDMA_CRC_Error_Count 0x003e 200 200 000 Old_age
Always - 0
200 Multi_Zone_Error_Rate 0x0000 100 253 000 Old_age
ne - 0
202 Data_Address_Mark_Errs 0x0032 100 253 000 Old_age
Always - 0

That is what I remember using even though it took almost a week to
complete, but it worked.

You didn’t have anything like 62485 Offline uncorrectable sectors that
time.

Bet it doesn’t this time.

Ah. I should open it up after I am done with it. Will I see able to see it

Yeah, I'd certainly have a look if it was mine.

or is very tiny like microscopic sized?

Nar, you should see gouged up full circles
on the media, where the head has crashed.

Might not tho if the head has just failed
electrically tho and can't read very well
anymore, but if that was the case you
wouldn’t see all the bads grouped together
as you do see in your previous much bigger
post of the error detail.