Reducing Size of the Previews File - Discarding 1:1 previews has no effect

[mystic_idea8889]

I moved my lightroom classic catalog to a new machine with a smaller SSD. The preview file had ballooned to 90GB. I started to discard 1:1 previews on older files but the file stays 90GB. It shows it's modified by this action with the "last modified date" but it persists 90GB, even after through multiple restarts. When does the discarded 1:1 data actually go away? Using LrC on MacOS Tahoe.

[johnrellis]

What is the setting of Catalog Settings > Previews > Standard Preview Size?  If it's more than half of the long dimension of a photo, then the 1:1 preview is retained as the standard-sized preview, and Discard 1:1 Previews won't delete any previews for that photo.

You can simply discard the 1:1 and standard-sized previews for all the photos, and LR will build them incrementally as you scroll through Grid view and the film strip.  Or, after discarding, you can select all photos and do Library > Previews > Build Standard-Sized Previews, letting it run over night.

[mystic_idea8889]

I've got it set to 2048, most long edge and most photos are 6000x4000. It's less 3000px so then shouldn't deleting 1:1 previews work?

[johnrellis]

"I've got it set to 2048, most long edge and most photos are 6000x4000. It's less 3000px so then shouldn't deleting 1:1 previews work?"

Yes. I just tried it with my test catalog of 600 raws, and it worked as expected.  I don't know what might be happening with your catalog.

[JohanElzenga]

How big is this catalog (how many images)? It's possible that the ballooning is not caused by 1:1 previews, but by standard-sized previews only. Depending on the catalog size, 90GB is not unreasonably large. You can simply discard all previews (not copy them to the new location, or delete 'previews.lrdata'). Lightroom will rebuild previews if and when it needs them.

[mystic_idea8889]

200,000 images, however many haven't been touched in years and if I go into those collections not even minimal previews show up. Kevin Rourke

[JohanElzenga]

90 GB is not excessive for a 200,000 images catalog. My catalog is about the same size (210,000) and my previews cache is around 250 GB.