Lightroom classic cache or preview is hammering hard disk for no apparent reason.

[kevin23304382mry0]

Since upgrading to Lightroom Classic 13.1,  the performance in the library and develop modules has become ridiculous.ly slow   I am running Lightroom classic on a Win11 machine with 32GB ram. My OS and lightroom catalogs are on NVME drives.  My photos are on a hard drive.    

Looking in Windows resource manager, it looks like if I click on a photo in lightroom, the Lightroom application is opening not only that photo but between 20 and 50 other photos in the same directory at the same time.  I can see this is causing massive disk contention.. Can you explain why Lightroom keeps doing this i.e why does it open 20 -50 files when I only want to look at 1.  

It does this on old and new folders...

[GoldingD]

How about a screenshot of that resource manager (manager, or monitor?).

[kevin23304382mry0]

Have attached an example.  So, it looks like when I go into the library module and click on a folder,  Lightroom is then generating full previews for each of the files which have thumbnails across the bottom of the Library module screen - which is typically 35 files as there are 35 thumbnails. If I scroll across the thumbnails so that thumbnails 36-70 are shown on the screen, Lightroom will attempt to read the next 35 original RAW files (presumably to generate full preview files).   If I try to click on a thumbnail, it can take a long time for the image to load on the screen (upto 30 seconds) because Lightroom is trying to already read upto 70 x 50MB RAW image files to create previews.

So I would to understand if this is expected behaviour (I.e should it attempt to create full previews of every file whose thumbnail is shown on the screen even if I  have not clicked on a thumbnail) or should it only try to create a preview file if I click on a Thumbnail.

The issue is happening on about 80% of my folders.  With some older folders (and a new test folder that I created and imported today),  Lightroom will only read a RAW file again if I click on a its Thumbnail.  For other folders, it seems to want to read all of the original RAW files again.

The "discard 1:1 previews" is set to 30 days and all of my folders  were originally imported with the minimal preview option. I have about 250000 photos dating back about 15 years. I have the camera RAW cache size set to 30GB. 

Looking in the Adobe 'Performance Optimization' documentation, it says that Lightroom will recreate previews for each folder the first time that you work on it if the Previews.Irdata file has been deleted or corrupted and so I am assuming that this must have happened during the upgrade to 13.1.  If this is the case,  does anyone know if I can get Lightroom to only generate a preview if I click on a thumbnail - rather than it generating previews for all of the files which have thumbnails showing on the current screen ?

[Conrad_C]

So I would to understand if this is expected behaviour (I.e should it attempt to create full previews of every file whose thumbnail is shown on the screen even if I  have not clicked on a thumbnail) or should it only try to create a preview file if I click on a Thumbnail.

By @kevin23304382mry0

As with many things in life, the answer to that is “it depends.” Specifically it depends on how certain preference settings have been set.

One is “Replace Embedded Previews with Standard Previews at Idle Time.” If this is enabled, then when the computer isn’t busy (that is, during idle time), Lightroom Classic will start building previews for any images that still have the previews embedded by the camera (which don’t show Lightroom Classic adjustments). Building those previews will naturally use computer resources. In the picture below, you can see that I like to keep this setting disabled. I don’t need to use up CPU and storage to pre-build lots of previews for images I might not need to view soon.

If this option is enabled, I’d expect Lightroom Classic to be observed using system resources during extended periods when you are not actively using the computer.

The other is “Generate Previews in Parallel.” If this is enabled, then when Lightroom Classic is generating previews for any reason (including, you enabled the option above, or you are viewing images in a folder or collection), it will try to do as many as it can at once. Of course, this requires putting multiple CPU cores into action. This will make the computer busier and possibly less available to handle other work, but the benefit is finishing the previews sooner. I leave this one enabled, because if I am viewing images, I would like Lightroom Classic to pre-build nearby previews from that folder or collection and take advantage of the available CPU cores to do it.

So, to round out the “it depends” answer:

If any background/parallel preview generation options are enabled, Lightroom Classic can be busy generating previews unrelated to the current image you are viewing.

If all of the options are enabled, Lightroom Classic can be busy generating previews even if you are not actually using Lightroom Classic at the time, and may use a significant amount of computer resources to do so, depending on settings.

If none of the options are enabled, Lightroom Classic might only generate previews for the current image you are viewing plus a few around it in the current source. This should be the lightest current load on the computer (other than Embedded Previews, which won’t show Lightroom Classic adjustments), but it also means you may have to wait to generate previews when you change the selected image or the source, if it isn’t going to be allowed to build then in advance.

A reason Lightroom Classic likes to at least build previews for the current source is to optimize “walking” down the image list from shot to shot. If it can pre-build, then when you click the next image in the same source, the preview is already ready so the image can come up right away. If it was not allowed to pre-build, then when you go from shot to shot there would be a longer delay as you wait for a preview to be built each time. New computers have so many cores that it seems to make sense to let those resources be used to get nearby image previews ready for you in the background, while you are staring at an image deciding what to do next.

[kevin23304382mry0]

Many thanks for the excellent explanation of preview generation. I checked my system and none of the options you mentioned are enabled however.

On my system, many of the photos are stored on physical disks and it seems that Lightroom is attempting to prebuild so many previews that the hard disk is struggling to service the IO for the currently selected photo . I can often see very high IO response times of over 200ms against the RAW file of the currently selected image.   .This often results in having to wait 10-15 seconds overall for an image to 'load' and zoom in on the screen. My CPU and graphics card dont appear to be breaking sweat whilst this delay is occurring.   

So , in absence of a way to limit Lightooms prebuild/prefetch  of previews, I will focus on the disk performance.  I know that my system did a large Windows update shortly before I upgraded Lightoom and there may be something in the update which is slowing the disk. Failing that, i will move the folders that I am likely to use  onto SSD/NVME. 

Thanks again for your help.

[Conrad_C · Accepted solution]

On my system, many of the photos are stored on physical disks…

By @kevin23304382mry0

Do you mean hard disks specifically (not SSDs)? Maybe that is the bottleneck, although many have reported that fast hard disks have been OK for storage of originals. I suppose it could be a bottleneck if it was trying to access multiple files on the same hard disk at the same time.

Many of my originals are now stored on a high capacity SATA SSD and I don’t seem to have a problem, but of course if you are moving onto NVMe SSDs that will be even faster.

[GoldingD]

• Do you have Face Detection running or paused?
• Do you have Address Lookup running or paused?
• Is their some other task running, that you would notice up in the Identity Plate?
• Are creation of Library previews running?

[kevin23304382mry0]

Face detection is not enabled.

Address lookup is not enabled.

There is no other task or progress bar showing for anything up near the identity plate.

I not sure what you mean by 'creation of library previews'.  Previews are seemingly  being created and stored for each of the 35 photos with thumbnails shown at the bottom of the screen when I click on a folder in the library module. If I click on another folder , it will read the first 35 photos on that folder. If I then click on the first folder again, it will not attempt to read the raw files for the first 35 photos so it must have created them the first time I clicked on the folder. 

Today, I have imported several other new folders and Lightroom is working as expected for the newly imported folders.  

[GoldingD]

In LrC, click on /help/System Info/ and copy the following section, then paste into a reply:

Application folder: C:\Program Files\Adobe\Adobe Lightroom Classic
Library Path: F:\My Photography\Events\Aviation\Airshows\NAF El Centro Air Show 2011\Air Show 2011-v13.lrcat
Settings Folder: C:\Users\DavidsLocal\AppData\Roaming\Adobe\Lightroom

Interested in the Library Path. I have a hunch that as a Windows user, you may have a MS account that you use to login to your computer, and as such you can trip up on OnerDrive. I have a hunch that the above path on your system may include /OneDrive/ in it. I will actually be happy if it does not.

[kevin23304382mry0]

Hi, I checked the library path and it points to  the lrcat file on my R: drive which is a local NVmE drive.  The applications and settings folder are both on the C: drive. I use a local account on the PC and do use Onedrive. In fact, most of the time the PC has its Nerwork cards disabled . I only enable them to do software upgrades or to validate licensing. Thanks for suggesting it though. 

[kevin23304382mry0]

Sorry - that should have read that I do NOT use Onedrive.