DDRescue taking months but no errors

Even though the question was asked 10 months ago, the answer might be relevant because the recovery cycle might still be running depending on a few factors! No pun intended.

The reason is that, time estimate is almost impossible, however sometimes you could get a rough idea as follows. One of the most obvious reasons is that you can't predict how long it will take the drive to read a bad sector and if you want ddrescue to read and retry every single one, then it could take a very long time. For example, I'm currently running a recovery on a small 500GB drive that's been going on for over 2 weeks and I possibly have a few days left. But mine is a more complicated situation because the drive is encrypted and to read anything successfully, I have make sure to get all sectors that have partition tables, boot sectors and other important parts of the disk. I'm using techniques in addition to ddrescue to improve my chances for all the bad sectors. IOW, your unique situation is important in determining time to completion.

By estimate of "loops", if you mean number of retries then that's something you determine by the parameters you use. If you mean "total number of passes", that's easily determined by reading about the algorithm here.. >man ddrescue< / Algorithm: How ddrescue recovers the data

I'll specifically speak to the numbers in the screen captures you provided. Other situations may have other factors that apply, so take this information as a general guideline.

In the sample you've provided take a look at ddrescue's running status screen. We get the total "estimate" of the problem (rescue domain) by "errsize". This is the amount of data that is "yet to be read". In the sample it is 345GB. Next line below to the right is "average rate". In the sample it is 583kb/s

If the "average rate" was to remain close to steady, this means you have 7 more days to go. 345 GB / (583 kb * 60*60*24) = 7.18 However the problem is that you can't rely on the 583kb/s. In fact deeper you go into recovery, the drive gets slower since it's reading more and more tougher areas and is doing more retries. So the time to finish exponentially increases. All of this depends on how badly the drive is damaged.

The sample you've provided shows a "successful read" was over 10 hours ago. That's saying that it's not really getting anything from the drive for 10+ hours. This shows that your drive may have 345GB worth (or a portion) of data shot. This is very bad news for you.

In contrast, my second 500GB drive that had just started giving me "S.M.A.R.T" errors, was copied disk to disk (with log file on another drive) and the whole operation took about 8-9 hours. The last part of it slowed down. But that's still bearable. While the very bad drive, as noted above is well past 2 weeks working on 500GB and still has about 4-5 % remaining to recover.

HTH and YMMV

You should probably wait until 100% completion before attempting recovery. According to the log viewer, ddrescue has managed to recover a scattering of blocks from various parts of the disk (the green areas), has found bad sectors in many areas (the red areas), and hasn't even looked at large parts of the disk (the yellow and blue areas).

The viewer shows the first part of the disk as having bad sectors. This means that ddrescue hasn't managed to recover the filesystem header or related metadata. Additionally, most filesystems scatter their data around the disk for performance reasons, so it's unlikely that many of the sectors that have been recovered correlate with the sectors that have data on them.

You might be able to speed up the "recover the easy parts" phase of ddrescue's operation by passing the --no-scrape or --no-trim options to entirely omit trying damaged sectors, or the --reverse option to read the disk back-to-front. You could also try playing around with values for the --skip-size option to see if larger or smaller values than the default (20 MB for your disk) will speed things up.