Today’s Question: I was using FreeFileSync this morning to backup my photo drive to some external drives. I realized that the Previews.lrdata file was huge at over 200MB. So, I added that file to the Ignore list and saved much time for the backup. So, the question: Can you see any reason to continue to back them up given that they’re transient anyway?
Tim’s Quick Answer: There’s no real reason to backup the previews file included alongside your Lightroom Classic catalog, since those previews could always be re-generated at a later date should you need to recover from a catalog backup.
More Detail: The previews generated by Lightroom Classic represent a cache, meaning they improve performance but can be considered non-critical in terms of backing up because the previews can be recreated at any time.
Of course, if you needed to recover from a backup of your Lightroom Classic catalog, and you have a large number of photos in your catalog, rebuilding the previews after recovering from a backup could require a significant amount of time. For example, I needed to rebuild previews for a catalog of about 250,000 images, and it took more than a day for the previews to build.
One could also argue that it is worth backing up the previews as a last resort option for recovering lower resolution copies of your photos should your primary photo storage be lost. But I recommend simply making sure that you have a reliable backup workflow to safeguard your original photos, so you don’t ever need to rely on the Lightroom Classic previews for this purpose.
Obviously, many photographers may prefer to simply backup everything rather than customizing their backup. But you can most certainly exclude the preview files for Lightroom Classic from your backup without any serious concerns.