Backing up your work in Lightroom is really simple. You can move your work in Lightroom from one computer to another pretty seamlessly now. Adobe has made this whole process very easy. In fact Lightroom is set to make a backup of your catalog once every week when it closes. It takes just a few seconds to have Lightroom back to the way it was after reinstalling on a new machine or even just after a recovery.
The files that are involved with the backing up Lightroom are in two parts. The first set of files you need to back up are the photos themselves, the second set of files is called the Lightroom “Catalog” The catalog is worthless without the source photos.
When backing up your photos for Lightroom you want to preserve as much of the folder structure as you can. Ideally you would have a simple tree structure to your folders where all your working folders are inside one enveloping folder. By doing this you can point Lightroom at your backed up copy of that folder and it will find all the image locations for your catalog. By default Lightroom does very well at categorizing your images. When importing from a camera Lightroom will create a folder for the year imported, and then subfolders for the days the images were taken. This works great because you can have all your imported camera images for the year organized in a single folder that is easy to copy. Ideally, you want all your camera files going into one folder that you copy for backing up, moving or restoring.
The Lightroom catalog contains a lot of data. The catalog contains all the previews and a record of every image in your Lightroom catalog. The catalog also consists of all the modifications to images you made in Lightroom using the current catalog. This is the beauty of non-destructive editing. Your original files are untouched and the edited version behaves like a filter applied over the original image. The catalog includes records of all the steps you did on each photo edit. The catalog is only a few hundred Megabytes, but the preview photos folder is big, it can be several Gigabytes in size.
Your Lightroom catalog itself is simple to back up. In OSX your catalog is by default in the /Users/(Your name)/pictures/Lightroom. In Windows the catalog is by default in the /Users/(Your name)/pictures/Lightroom. It's best to back up the whole /Lightroom/ folder. To find where you catalog is saved to go to (Edit<Catalog Settings)
Once there you can find the working directory of your current Lightroom catalog. You can also set up different Backup schedules and a few other things. "File Handling" refers to how Lightroom generates and stores image previews.
Recovering or using a catalog is really easy. To recover a backed up catalog you first need to have your source images available on the computer. By going to (File>Open Catalog) in Lightroom you can then navigate to where your backed up catalog is and select it. The catalog extension should be ".lrcat" As soon as you select your catalog you will have images start popping up from that catalog if you saved the preview folder as well. The problem is...those aren't actually your images, they are previews.
If you go to your "Library" page of Lightroom you will probably see question marks. This is because Lightroom is telling you that it can't find the source images. Not to fret, over on the left in your "Folders" menu there will also be question marks if your folder locations have moved. Your library contained all the locations of all your photos. Right click on a folder and click "Find Missing Folder." Point Lightroom to the new folder location and it will hunt for any images that should have been in that folder. Easy as pie.