Backed Up Catalog - Where are my Photos?

Question

Hi,
I back up my Lightroom 5 catalog in several ways.  I'm on a Mac and keep my catalog on one external drive while backing up to two other external drives.  One of my backup methods is to simply drag and drop the Lightroom 5 Catalog folder to another external drive.  This seems to bring everything in that folder, including the .lrcat file and all image files, with it. 
However, if I open Lightroom from the backup drive by clicking on the Lightroom 5 Catalog.lrcat file there, and the drive holding my original catalog is off, the thumbnails that appear for most of my images in grid view are empty.  Most of the metadata are there, but the File Size item reads "File not found".  This is true even for those images that show up in their thumbnails.  On the other hand, if the drive holding my original catalog is on, all the thumbnails have images and the metadata no longer say "File not found".
I'm assuming this is some sort of referencing issue, with Lightroom looking for the original image files even though I'm opening it from the backup drive and the backup drive contains its own copies of the image files. 
Bottom line is that I'm not sure now that copying my entire Lightroom 5 Catalog folder by dragging and dropping to another drive is a good backup procedure.  (I also use Time Machine to back up everything to another external drive.)  If I lose my main drive that contains my original catalog, will I be able to get my backup to look for the image files on the backup drive?  If so, how would I do that?
Thanks for all responses.

Answer 1

When referring to the "catalog" in Lightroom, we are usually talking about the Lightroom catalog which is a database. It keeps track of where the images are located on your computer as well as any adjustments that are made to those images. In my opinion, it is a good idea to always allow your backup Lightroom catalog files point to the original images that you are working on using Lightroom. Otherwise, you can have several different versions of the same image. The idea of the image backup is to have something to fall back on in case of a disk or computer crash.
If you really want to redirect Lightroom to the backup images then it would be a good idea if all of your images were in a folder structure that puts all of your image folders within one master image folder. Then, in the backup catalog, you could right click on that master folder and choose the option to "update folder location" and you would be able to point Lightroom to the backup files. By doing this on the master image folder, it will update the location for all subfolders and images. But as I indicated, I think it's a better idea to leave the backup Lightroom catalogs pointing to the images in their original location. Otherwise, if it becomes necessary for you to use a backup catalog because of catalog corruption, the backup catalog will be pointing to the backup images which might not have all the adjustments.
A couple of examples might help explain a little better. Let's assume first that you encounter a corrupted catalog. All that's necessary is for you to replace that corrupted catalog with your most recent backup. If the catalog is still pointing to the original images then you can simply resume your work. Of course you will have lost any changes that were made since that backup was created. So let that be an indication of how often you decide you want to backup your catalog.
Now let's say that your catalog is okay, but your images are on a hard drive that crashes. Then all you have to do is point the catalog to the backup images and all of the adjustments in the catalog will be applied and work can continue uninterrupted. You might want to copy those backup images to another new working hard drive. If the hard drive has the same name or drive letter as it did previously you will just continue working. If to drive letter changes all you will have to do is update the folder location. All of the adjustments will still be in place and work continues.