I am using Lightroom 2 on a PC laptop with Windows 10. There may be errors with how I recall the problem, as it took root over a year ago.
A while back I had 2 drive failures within a fairly close timespan (about a few months) and I didn't have time in between them to consolidate all my data onto a single drive, resulting in all my data being spread across 3 drives (A - the main drive, and B/C, two back up drives from the repair places). There were duplicates of files on all 3 drives (A to B and B to C), but no single drive had a complete copy of all my files. This carried through to Lightroom, where I'd been importing images from specific subfolders on each drive rather than finding all images in one folder or one drive.
Earlier this year, I was finally able to consolidate everything onto one drive (and also do a complete backup), but I couldn't figure out how to get the folders in LR to point to one drive. When I tried to change the file association for a missing file, I'd keep getting an error message saying the "new" file already existed in the catalog (I think because at some point I'd asked LR to import all the images one one of the drives). This meant that while the file existed on a drive and also in LR, the edits stored in the LR catalog wouldn't point to that file.
I eventually found a tutorial on how to change the file association and I did this for what I thought was all the LR folders/collections, and then I went to delete the unneeded drives from LR. Well, I must have missed a few collections because I then watched in horror as the file counts in several key collections went down to 0 and I lost my edit data (I think). I did my best to research a way to undo what just happened, but everything I found told me that once this happened, you couldn't undo it. No article I'd found suggested trying to import a backup catalog from before this issue happened, and for whatever reason it didn't occur to me to try this, so I just cursed my life and moved on. Until that point, I rarely revisited old collections to add files to them or re-edit them anyway, and at least I had the finished exported files, so I figured "Oh well!" Of course that has now changed, and I'm finding myself having to revisit several older collections to add/modify files and try to edit the new additions so they are consistent in appearance with the older finished files.
Recently, while researching an unrelated issue, I found a tutorial on how to merge an old catalog with a new one, so I started a new master catalog and have begun trying to import older catalogs into it, starting with the catalog I found dating to just before I lost my collections. However, after running that import for more than a day (there are about 120K images in it), it came up in an error where more than half the images didn't import.
So...before I do anything more to stir this rat's nest, I'm consulting this forum for advice.
Thanks for your help!
I'm not sure what to say for "advice", most of the problems have been either because you made a mistake, or your computer hardware has had issues.
However, after running that import for more than a day (there are about 120K images in it), it came up in an error where more than half the images didn't import.
Since you didn't tell us what the error message said, we would need to know that if you want us to help.
Long term, you want one catalog with ALL of your photos, it doesn't matter if the photos are on multiple drives, that's simply not a problem. This one catalog and all of your photos needs to be backed up on a regular and automated basis, and the backups must go to a different drive than the originals.