There couldn't be changes. I make sure of that by mounting the drive as read-only, so that LR cannot ever change any file or even add stuff to the source directories, so no XMP is possible either. This time I moved files from an external drive to an internal drive and when relocating the files in LR, it put up all the warnings. Changing originals on disk, even if it only supposedly the metadata, is wrong. File dates change, the metadata will have the software name and they won't even look like files that camera from a digital camera anymore. On top of the risk of a change being harmful.

@Re "no changes", at least the dates change when you move files on disk outside of Lightroom. That may be all it's complaining about.

@Re: changing originals being "wrong," maybe you shouldn't be using Lightroom, since you clearly don't trust it with your data. Lightroom is inherently not a catalog-only program: it does depend on being able to store metadata in the file, so that "Edit in Photoshop" and the like work properly. There are probably other photo management apps that purposely keep all metadata in their own catalog only. That would annoy me, but it sounds like that's what you want.

Specifically, I am worried about changing my files, not just the metadata. I have a workflow that has been working very well so far, although it might not be perfect, it fits very will with how I do backups and other tasks. This time I did do something different and that was travelling with a laptop, so I moved the files from the external drive to the internal drive after doing a Export As Catalog and then Import From Catalog. Essentially I almost did what you describe in the 3 last steps, except for not exporting the negatives. Maybe that would have avoided the problem.

OK. Is there anyway to know what LR is complaining about? I could try to have a script run over everything and set the date properly if that is what happened.

I gave you the procedure: use exitfool and diff.

To me LR being non-destructive is exactly why I would never expect it to change the files but if there are software that work better that way, I don't know which but I will investigate!

Lightroom is nondestructive. Writing XMP data back to the image file does not "destroy" the original unless your disk subsystem is broken, and that's not Lightroom's fault.

Personally, I'd like to see an option for external XMP files with JPG, DNG, and such, but Adobe doesn't want to do that, so...

If you're using proprietary RAW files instead of DNG, then you do force Lightroom to use external XMP, which leaves your original files absolutely untouched.

@WarrenYoung Hi Warren. You're right the XMP in themselves would be fine since obviously they are external to the original.

I've been using Lightroom since before 1.0, and it has never once destroyed an original image. I've had "Automatically write changes into XMP" enabled the whole time, and I was also an early adopter for DNG, so external XMP is an extreme rarity for me.

I've got over 400,000 images in Lightroom.

Also been using LR for quite a while, not sure if it was 1.x or 2 but it has always worked for me using the readonly partition for source. This ties in to how I started doing backups in that old directories for media do not get revisited, so if new files were to appear there or change, it would be a serious problem. This has nothing to do with LR of course.

Before you leave the Lightroom world, realize what you'd be giving up: the ability to move your files to another app. XMP is an open standard, which means many apps — including exiftool — can read the metadata. If you trap all your photo metadata inside an app's proprietary catalog, how do you get it out?

Well, that's how I consider my images with LR! All my metadata is in there.

I would really like to have a contingency plan for LR too. I don't think its possible right now. If LR stopped working or became too expensive, how would I get to my processed images? Would XMP even help for that?

That includes ratings, labels, keywords, and even develop settings. (I wouldn't expect anything but Adobe apps to understand Develop settings, being tied into the ACR engine, of course.)

My solution to the processed images problem is Jeffrey Freidl's folder and catalog exporters, which I configure for high-quality JPEG output in folders that parallel the originals.

That's what I thought. I don't see a way another app could interpret this, maybe a coarse approximation.

Yes, you export full-res JPEG of everything just to be safe?

The exported folders get sync'd off-site, so that even if my house gets hit by a meteor, I've got full-quality finished versions of all high-rated photos. (3 stars+.)

Ah, yes, OK. I do something similar, exporting all JPEGs at full-res for 3* and up and that one goes into one of the writable directories which gets backed up periodically. It keeps size manageable. I would not periodically backup all the photos, only incremental, which is why it would trouble me to have XMPs appearing there and changing from time to time. Any chance there is a way to tell LR where to put XMPs, in a parallel structure?

About the only thing I lose that way is the ability to readjust the brightness levels, but once a photo hits 4-5 stars, it isn't likely to ever be readjusted, ever. There's a tiny chance I could go back and improve a 3 star image to be 4-5 stars that way, but realistically, once it's exported, it probably isn't going to get better.

That sounds reasonable. It is extremely rare for me to edit back files once I did it after importing. It did happen this year when I went through a dust-busting phase on old photos :)

The Friedl export plugins only export changed images. If the metadata changes, that will of course trigger a full JPEG image export for that one photo, but that's what you want. (Actually, it's configurable: you can tell it to ignore certain metadata changes.) As for backups, any decent backup program can scan the source folder and copy only the changed files.

Another option you should be looking at is exporting images from Lightroom to a cloud backup folder, since that is inherently off-site and incremental.

Re: dust-busting, you don't need raw images to do that. I do it on exported JPEGs from time to time.

XMP is either written into the image file itself (JPG, TIFF, DNG, PSD) or in a file alongside the original. If it were otherwise, other apps couldn't find the XMP data, which would negate its purpose.

I think you need to be looking hard at the risks that caused you to create this read-only drive problem in the first place, not trying to arm-twist Lightroom into coping with it. What is it you don't trust exactly? Is it Lightroom? Malware? The OS? Yourself? Fix the actual problem.

Well, sounds like I have to check that magical plugin. Cloud backups are a bit of the long way out for me. It's not the problem of finding out what to backup, I can do that with rsync, but it is that I avoid copying the same files just to make another backup. My system is divided into a relatively small set of disks that get backup repeatedly (things that change), plus large disks that only get incremental backups (things that get created but never change, aka images).

Plugins: regex.info/blog/lightroom-goodies

I'm talking about "Collection Publisher" and "Folder Publisher". You can probably get away with only one, chosen based on how you want to specify the files to export.

Great! I just just going through the list and it seemed like a lot to sift through.

Going through a reevaluation is fair but it's also high impact, so it will certainly take me a while to change the way everything works around here :)

Got to go soon. Thanks for all the suggestions!

One final thought: if you're on a Mac, have you considered using OpenZFS on your external drives? (Or, wait for APFS, which will get you some of the ZFS benefits.) Its snapshotting features may get you as close to read-only disks as you really need, in that any changes cause a second copy of the file to appear, with the old one still retrievable via the snapshot.