The transition may be complete: I may have my local photo library both easily accessible, and frequently backed up in two different locations.
I say may because I do not want to mark this project as complete until I have actually seen both stages of backup finish and look good. The first step is running right now, the second one will run in the middle of the night. So I have a reminder to check them both in the morning, and then we may be able to celebrate (and perhaps also begin to contemplate things like Icloud photo library).
What did you do, then?
When last we discussed my situation, I still lacked backups, and my library was on the right disk but still wrapped in a disk image which just made everything that little bit more unwieldy.
Getting off the darn disk image was by far the more time and patience-consuming step. Since dragging the library from the sparse image to the disk itself always failed, I figured I needed to involve another drive in some way. Fortunately, I could get hold of an identical SSD which had not yet been put into service for anything else. Copying the disk image over to that drive was completely painless. I am still a little bit in awe of just how fast local data transfers between two modern SSD:s are.
All good: another backup of the library, and another destination from which to move. Unfortunately, dragging from disk to disk produced the exact same kind of error and failure as dragging from the image to the disk did.
All right, how about compressing the library, moving the compressed file to the right place, then unpacking it right there?
This actually turned out to be the working solution, the only catch of which was a little sliding puzzle style game of storage management. No drive had enough space for the disk image, the compressed library and the unpacked library, and the internal drive had just a hair to little space to fit the compressed library. So what I had to do in the end was compress with one SSD as the source, the second one as destination, then go in to the destination and delete the disk image with its copy of the photo library before unpacking.
Of course, Macos facilities for working with packing and unpacking files are not exactly feature rich, so I ended up using tar (of all things) in the terminal to compress straight from one drive to the other. It was probably a dumb and inefficient choice in many ways (during the whole process, dinosaurs kept gathering outside my window to stare at the backward, comet-denying computer guy inside), but it was really easy to dig up an example of the right settings, and it ran as reliably as ever.
One decompression later, and everything was finally the way I wanted it: Photo library, right there on the disk, no intermediary disk images or other unnecessary cruft.
Last but not least: backups
Superduper could indeed solve backup to the NAS for me. I have now for the first time scheduled it - so late at night every weekday it will wake up and back the whole photo library up to my NAS. Once there, I already have Backblaze set up for a small selection of important things, so the final step was simply to add the new backup files to the list.
And here we are.
Tomorrow, we check logs.