Can't Delete Previews

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CameraCarl

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My 2017 27inch Retina iMac has only a 500GB SSD and about 200GB of it is taken up with Lightroom Previews. I decided to delete the 1:1 previews, but Lightroom won't let me. I tried Lightroom>Library>Previews>Discard 1:1 Previews and then I clicked on Discard All. The status bar showed Discard 1:1 Previews and after a few minutes ran its course. Then I checked my computer storage capacity and nothing changed. So I quit and restarted Lightroom. Still no change in computer storage. So I restarted the computer: no change in storage. So I tried highlighting all the images in my Lightroom catalog. And again Lightroom>Library>Previews>Discard 1:1 Previews>Discard All. Again the status bar was working for several minutes and when it stopped, I checked the computer storage. Again no change. So restart Lightroom and restart computer. Still no change. Then I did the same for Smart Previews. No change. And, just for luck, a third time I tried deleting the 1:1 previews as described above. Again no change. So I'm stumped: just how do I get the Lightroom to delete its previews?

Mac OS Big Sur v 11.6.3
iMac (Retina 5K, 27-inch, 2017)
Radeon Pro 575 4 GB
40 GB 2400 MHz DDR4
 
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My loose understanding from very old discussions about this is that LR takes its time and does this as a background task, and not something immediately visible. I'd suggest doing what you did, then leaving lightroom running over night, and see if that works.
 
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My 2017 27inch Retina iMac has only a 500GB SSD and about 200GB of it is taken up with Lightroom Previews. I decided to delete the 1:1 previews, but Lightroom won't let me. I tried Lightroom>Library>Previews>Discard 1:1 Previews and then I clicked on Discard All. The status bar showed Discard 1:1 Previews and after a few minutes ran its course. Then I checked my computer storage capacity and nothing changed. So I quit and restarted Lightroom. Still no change in computer storage. So I restarted the computer: no change in storage. So I tried highlighting all the images in my Lightroom catalog. And again Lightroom>Library>Previews>Discard 1:1 Previews>Discard All. Again the status bar was working for several minutes and when it stopped, I checked the computer storage. Again no change. So restart Lightroom and restart computer. Still no change. Then I did the same for Smart Previews. No change. And, just for luck, a third time I tried deleting the 1:1 previews as described above. Again no change. So I'm stumped: just how do I get the Lightroom to delete its previews?

Mac OS Big Sur v 11.6.3
iMac (Retina 5K, 27-inch, 2017)
Radeon Pro 575 4 GB
40 GB 2400 MHz DDR4

The filesystem is going to hold deleted files in Trash and these will take up space until you empty Trash.

A better option would be to delete the whole previews folder and let Lightroom Classic rebuild previews as you request them. Many of the earlier previews may never be accessed again unless you export or print these mature images.

If you are stuck with an undersized SSD, time to upgrade. Either just get a new primary disk, a new computer or a new EHD.


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LR will only discard a 1:1 preview if its width is 2 or more times the width of your standard-sized previews; otherwise, LR keeps the 1:1 preview to use as the standard-sized preview.

Chances are, given your display, 1:1 previews of your photos are less than twice the width of the standard-sized previews. To verify:

- Please post a screenshot of Catalog Settings > File Handling.

- What are the pixel dimensions of most of your photos in your catalog?
 

CameraCarl

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Thanks to all so far for the help.
There is nothing in my trash to empty.
A screenshot is attached.
My catalog has files going back to 2005 but a random sampling of files from the last 5 or 6 years has file sizes of 5472x 3648 and 6720x4480
A new computer... wouldn't that be nice, but who has $2500? Adding a new internal drive in a four year old iMac doesn't make financial sense at Apple Store prices. Maybe a new external SS might be doable if I can't fix this with what I own. I'll have to reread how to move a LrC catalog to a different drive if I can't fix this.
 

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The screenshot shows the standard previews are size 5120, and your photos are 5472 - 6720 in width. So the 1:1 previews are less than twice the standard-preview size. Thus LR is using the 1:1 previews as standard previews, and it won't discard them. You could delete the entire previews cache and rebuild them from scratch, but that won't save much space, since the standard previews are close in size to the 1:1 previews.
 
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What you can do is take two steps:

1: Simply delete the entire ‘catalogname previews.lrdata’ file
2: Start Lightroom, go to Catalog Settings, and change the standard previews size from ‘Auto (5120)‘ to 2880 pixels

A short explanation of the second step: Lightroom has a long standing issue (I’d call it a bug) with preview sizes and image display on high resolution monitors. It’s a long story, but if you are interested I can post the details here. I have sent a long report to the Lightroom product manager at Adobe, so I hope they will finally have a look at it. For now this is the only thing you can do to keep your previews size down.
 

CameraCarl

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I think I understand the problem. I'm going to do as Johan suggested and delete the lrdata folder; then change the preview size. Next I am going to start shopping for an external 2TB SSD to connect to the computer to use for my Lightroom catalog and previews. Once I do this I can transfer my catalog and just use the interrnal SSD for routine stuff. I would like to thank everyone for your insight and assistance.
 
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