It’d be more space efficient to store a COW2 of Linux with a minimum desktop and basically only DarkTable on it. The VM format hasn’t changed in decades.

Shoot. A bootable disc containing Linux and the software you need to access the images, and on a separate track, a COW2 image of the same, and on a third, just DarkTable. Best case, you pop in the drive & run DarkTable. Or, you fire up a VM with the images. Worst case, boot into linux. This may be the way I go, although - again - the source images are the important part.

I’d be careful with using SSDs for long term, offline storage.

What I meant was, keep the master sidecar on SSD for regular use, and back it up occasionally to a RW disc. Probably with a simply cp -r to a directory with a date. This works for me because my sources don’t change, except to add data, which is usually stored in date directories anyway.

You’re also wanting to archive the exported files, and sometimes those change? Surely, this is much less data? Of you’re like me, I’ll shoot 128xB and end up using a tiny fraction of the shots. I’m not sure what I’d do for that - probably BD-RW. The longevity isn’t great, but it’s by definition mutable data, and in any case the most recent version can be easily enough regenerated as long as I have the sidecar and source image secured.

Burning the sidecar to disk is less about storage and more about backup, because that is mutable. I suppose an append backup snapshot to M-Disc periodically would be boots and suspenders, and frankly the sidecar data is so tiny I could probably append such snapshots to a single disc for years before it all gets used. Although… sidecar data would compress well. Probably simply tgz, then, since it’s always existed, and always will, even if gzip has been superseded by better algorithms.

BTW, I just learned about the b3 hashing algorithm (about which I’m chagrined, because I thought I kept an eye out on the topic of compression and hashing). It’s astonishingly fast - for the verification part, is what I’m suggesting.