Today’s Question: I don’t recall you ever talking about the HUGE space that the full-size previews [for Lightroom Classic CC] eventually take up on one’s computer hard drive. I know how to move the catalog (not that large) to another external drive, but I could not find out how to move the previews to an external hard drive to save space on my computer. My previews take up 100 GB!!
Tim’s Quick Answer: All of the previews for your photos in Lightroom Classic CC are actually stored in a file alongside the catalog file. As a result, if you move the entire folder containing your Lightroom catalog file, the previews will come along with the catalog.
More Detail: Lightroom creates previews of your photos to speed up the process of reviewing images. There are a variety of different previews available, including the option to generate full-resolution (1:1) previews. As the number of photos in your catalog increases, the previews files can obviously get quite large. That is especially true if you generate full-resolution previews for some (or all) of your photos.
The catalog file has a filename extension of “.lrcat”. Alongside that file you will also see a file that contains the previews for your images. That file will have the same base filename as the catalog with the word “Previews” appended to it, and this file will have an “.lrdata” filename extension.
As long as the previews file remains with the catalog file, Lightroom will be able to find the previews that have already been generated. So, you can move the folder containing the catalog file to a different storage location, and the previews will be included with that transfer.
To actually move your Lightroom catalog to a different location, be sure to first close Lightroom. You can then move the folder containing your Lightroom catalog to the desired location. To quickly open Lightroom with the catalog in the new location, you can simply double-click on the catalog file (with the “.lrcat” filename extension) to open Lightroom using that catalog.
Note, by the way, that you can also have Lightroom automatically purge full-resolution previews after a set time interval, to help keep that particular previews file from getting too large. To review this setting, bring up the Catalog Settings dialog by choosing “Catalog Settings” from the Lightroom menu on Macintosh or the Edit menu on Windows. On the File Handling tab you can then select how soon you want full-resolution previews discarded from the popup labeled “Automatically Discard 1:1 Previews”.