I'm currently transferring my Lightroom catalog from my laptop to my new desktop PC. I decided to copy both the catalog file itself and the preview files (folder Lightroom 3 Catalog Previews.lrdata). I've been really astonished about its size and the number of files it contains: it's nearly 3 GB and contains over 40.000 files for a catalog that contains about 8.000 photos. In the catalog options I have chosen Automatically Discard 1:1 Previews > After 30 Days, so I would expect LR to delete previews that haven't been needed for 30 days. Still, the folder contains files that are over 2 years old and haven't been accessed for over 2 years.

I have well noticed the following from the Adobe site:

Note, however, that the file that contains the previews, the [Catalog name] Previews.lrdata file can grow large if you have the option to delete previews set to Never or 30 days.

But this does not explain, why the previews folder contains files with "old" access times.

Therefore my question: why does the preview folder grow so big and how can I prevent this in the future?


AFAIK LR keeps every preview you have. You can only optionaly delete 1:1 previews because of their huge size. But it will keep the little ones.

Previews are kept because when you disconnect HDD with images you still must able to view images in grid view. This is Adobe's idea...


Have you run Optimize Catalog? I'm not sure why those previews seem to still be there after 30 days, but there would have to be some sort of background process running to look for "expired" ones - perhaps that only kicks in if you optize the catalog or start running out of space in the cache?

If you are migrating, I wouldn't copy the previews folder, just let LR regenerate them in the new PC. You may have a different resolution on the PC, and might want to optimize the previews for that resolution.

  • I do the planned catalog backups weekly and have the Optimize catalog option checked. But I will give it a try and see what happens. Thanks for the tip with the new resoulution previews.
    – Deve
    Apr 14 '13 at 12:37
  • I've just tried the catalog optimization but unfortunately it didn't reduce the size of the previews folder.
    – Deve
    Apr 14 '13 at 15:54

My file with previews, with the extension .lrdata, was about 15GB. I changed the settings to what I would expect would result in the smallest possible file, to no effect whatsoever.

Instead, I deleted the previews file and had Lightroom regenerate the previews when necessary. My current previews file is 10MB.

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