Yes, you can move the catalog file to the external hard drive. You will have to open the catalog from the external hard drive.
Also, Lightroom works only with catalog. So, the catalog file is required to use Lightroom as it records all the edits, reference of the images and the metadata. Without the catalog file, you will only have the image files without any changes made.
Please follow the below link to get more information about catalog.
Hope this helps.
Thank you so much. In order for me to clarify, I can move the Catalog and the Catalog Previews.lrdata to an external drive and keep the Catalog Smart Previews.lrdata on my laptop hard drive. What about the Temporary Import Data? Should those also be moved or can they reside on the laptop with the Catalog on an external hard drive?
Keeping Catalog Smart Previews.lrdata folder separately is of no use.
Catalog Smart Previews.lrdata and Catalog Previews.lrdata files are only accessible if the Catalog file are stored together.
If temporary import data files are not in use and the system is not using these files you can go ahead and delete those.
Please let us know if this helps.
If you are trying to save space, get rid of the smart previews, as you don't need them as long as the original photos are available on some disk that is connected to your computer.
You can control (somewhat) the amount of space taken up by the regular previews using the options in Catalog Settings->File Handling tab.
Now I really do not understand! I was told that you can keep the Smart Previews on a separate drive than your Catalog in order to save space. I was told that when you connect your Catalog to the Smart Previews it automatically makes all of the Develop changes you made to the Smart Previews. If the Smart Previews has to be on the same device as the Catalog Previews.lrdata, requiring about twice as much space as that file, then what is the purpose and benefit of the Smart Previews? The only reason I bought Lightroom was to have the space saving capability of the Smart Previews and not have to have the entire catalog on my laptop hard drive!
The catalog file (*.LrCat) contains your metadata, your edit instructions, and references to your original image files. (The images are not "in" the catalog.)
Associated with the catalog is a "previews.LrData" folder. This directory tree contains the thumbnails and small preview files used to display your images within Lightroom.
To edit an image, LR needs access to the original image file. If you know that the original files are not going to be available -- say on an unplugged external drive -- then you can have LR create "smart previews" for these original files. These smart previews are stored in their own directory tree in the same folder as the catalog file, in addition to the "previews.lrdata" tree.
If you want to share the catalog with multiple computers, you can put the catalog on an external drive with your original images and move the drive from computer to computer using the catalog and images from the external drive. This also prevents the need for smart preview files since the original files are available. Since the catalog is used from the external drive, the "previews.lrdata" tree will also be on the external drive.
Now I really do not understand! I was told that you can keep the Smart Previews on a separate drive than your Catalog in order to save space.
Then you were incorrectly informed. The Smart Previews can be used to save space only in that you can use them with the catalog file when you don't have access to the original files. Thus the original files can be on a drive not connected to your computer but by using the Smart Previews you can still work on them.
If this is not a saver for you and you're always going to have the original files connected then, as DJ has already said, you can delete the Smart Previews altogether. You could also look at the settings for your ordinary previews. As well as their size you can choose how long they're kept. They can always be rebuilt when needed as long as you have the original files.
Does that mean that I can keep the Catalog and Smart Previews on my laptop hard drive and the original photos and Catalog Previews.lrdata on an external hard drive that is not always connected to my laptop and still view and develop the Smart Previews on my laptop?
Does that mean that I can keep the Catalog and Smart Previews on my laptop hard drive and the original photos and Catalog Previews.lrdata on an external hard drive
Catalog, previews and smart previews need to be on a drive that is connected to your computer, and they all must go on the same drive; original photos can be on a drive that is disconnected.
Back to your original question, if your internal hard drive is getting full, then you want to move the Catalog, previews and smart previews to the external drive. Again, if your photos are always on a connected drive, you don't need smart previews at all.
Paige has pointed to the right way.
Smart Previews are basically used by the customer who does not have the images always connected to the computer.
Please follow the link below for more information on Smart Previews.