It’s described here. It’s basically making a dummy dlist with no files listed, to get Recreate to populate block information into the DB so that blocks already uploaded are reattached to any files that have those blocks…
It’s basically replacing one file in a .zip file. It sounds like you encrypt, but using AES Crypt can do that part.
It’s just a Recreate helper, and risks were discussed earlier. Basically, if you mean source data you’re fine.
Recreate button, if blue, will delete the DB thus it can’t think of deleting remote files (which are less critical than source data, and in fact if this doesn’t work we’re probably going to have to throw away the partial…).
If DB is not present at all, I think Recreate won’t go blue, but Repair button will turn into database recreate.
Assuming this loads block info successfully, you’d want to watch some of the files that go by on the home screen or live log at verbose level, and at least do a test restore of those to see if they backed up properly.
So none of this should endanger source files, but it’d take more doing to get convinced that backup is fine. What I’d probably do if you’re up for trying to save two weeks of uploads is do some more testing myself…
One advantage of the two-weeks-then-fail plan is it could generate a log that might show what went wrong. Going that route should probably bump blocksize up from its default 100KB, because 3 TB of 100 KB gets 30 million blocks for the database to track, and it slows down operations (Recreate shows it quite heavily).
Especially given video which doesn’t deduplicate well, something like 5 MB blocksize might be reasonable.
Choosing sizes in Duplicati gets into this some. A big note is blocksize on existing backup cannot change, which possibly will drive this effort into a 1 TB reupload just to get the blocksize more appropriate for 3 TB.
But this other path should be pretty fast to play with, and we might learn something without a 2 week wait:
Trying to read current upload back into a DB might be interesting to see if it even starts, fails soon, or does another two weeks. Is network simple (e.g. typical home network) with no boxes in the middle to time out?
Trying to debug something that takes so long to fail is certainly awkward, and I don’t know where it’ll land…