Lightroom Classic 15.3.1 on iMac OS 15.7.7 (SS 2TB with 824 GB available) does not display thumnails until they are selected. lrcat size 4 GB. Previews.lrdata 29 GB

Forum|Forum|1 day ago
June 30, 2026
2 replies
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It’s not that the thumbnails are slow to display; they never display until they are selected. Images are stored on an external drive. The catalog is on the iMac SS.

Correct answer JohanElzenga

Unfortunately, yes. You don’t have to do that manually, however. You may not view a lot of your old images anymore, so there’s no need to generate previews for them. Leave it to Lightroom. It will rebuild previews only if and when needed.

By the way: if you have 700,000 images, and the previews are only 29GB, couldn’t that mean that you caused this problem yourself by setting the preview cache size in the catalog settings way too low?

lowellnelsonAuthor

Inspiring

Well, I haven’t set a limit to the Preview cache size.

JohanElzenga

Community Expert

Then most of your older photos probably have no previews, because 29GB for 700,000 photos is very little. Anyway, it doesn’t matter for the problem and the possible solution.

-- Johan W. Elzenga

JohanElzenga

Community Expert

Your previews.lrdata may be corrupted. Try this: move the previews out of the catalog folder and then start Lightroom. Lightroom should rebuild them, so you should see them appear one by one.

-- Johan W. Elzenga

lowellnelsonAuthor

Inspiring

If that turns out to be so, does that mean that previews will have to be rebuilt for all of the 700,000 images in my database?

JohanElzenga

Correct answer

Community Expert

Unfortunately, yes. You don’t have to do that manually, however. You may not view a lot of your old images anymore, so there’s no need to generate previews for them. Leave it to Lightroom. It will rebuild previews only if and when needed.

By the way: if you have 700,000 images, and the previews are only 29GB, couldn’t that mean that you caused this problem yourself by setting the preview cache size in the catalog settings way too low?

-- Johan W. Elzenga

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