Why does 'previews' slow the process of baking up Lightroom files?

[Ken Nielsen]

I need an expert's opinion and advice.... What would normally take just a few minutes now goes on for hours of incredibly slow backup time when it gets to this... 'presets' part of the backup of the lightroom catalog. Is it necessary to include this? My take on it is that it is incredibly encrypted so it making the backup software work hard to actually reproduce and backup... Yes, it does backup successfully and eventually, but I'm thinking I'm wasting time backup up the Lightroom catalog this way. Not backing up the actaul files as they are on external drives but just the 'catalog' that Lightroom uses to locate and sort and organize what is in the catalog. Someone who understands what is going on, do I need to go through this long abnormal backup process of 'presets', or, do you have anything to say or recommend... Tia, Ken

[Claire H. · Accepted solution]

Hi @Ken Nielsen, Thanks for reaching out! If I understand the issue you're experiencing, here are a few recommendations to help speed up the process:

1. Exclude Presets from Backup: If your backup tool allows folder-level exclusions, consider excluding the Lightroom Settings or Presets folder. If they're important to you, ensure you have a separate backup strategy for them.

2. Optimize the Catalog: Before backing up, go to File > Optimize Catalog. This can reduce the size and complexity of the Catalog, which may help with backup speed.

3. Use Faster Storage: If you're backing up to an external drive, ensure it's a fast SSD connected via USB-C or Thunderbolt. Slow drives can bottleneck the process.

4. Split Large Catalogs: Consider archiving older projects into separate catalogs if your Catalog is large (e.g., 50GB+). This can reduce the size of your working catalog and speed up backups.

5. Keep Lightroom Updated: Adobe occasionally improves backup performance in updates, so make sure you're running the latest version

If you're still experiencing issues with your backup speed, please let us know, and we will continue to look into it. I hope this helps! ^CH

[Ken Nielsen]

Thank you... These 'presets' seem to be the problem and from what I gather, they are not needed as a part of making a backup as Lightroom will reconstruct them if they are missing? Is that true?

[Conrad_C]

See my reply below…it is not about presets, it’s about the Previews file. Focus on the
"…Previews.lrdata" file that your screen shot clearly shows has grown to occupy over 3/4 of a terabyte!

Yes, the Adobe reply missed this critical point. It talked about excluding presets, but doing that will not save you any time or backup space. Previews are the problem, not presets.

(Presets take up almost no space, previews can potentially take up many GB of space.)

[Ian Lyons · Accepted solution]

You appear to be using a third party backup solution. The built-in LrC backup backs up '.lrcat' and '.lrcat-data''. Previews are not included because they can be rebuilt.

> do I need to go through this long abnormal backup process of 'presets', or, do you have anything to say or recommend

No you don't! Use the built-in backup!

[Ken Nielsen]

I'm using the built-in backup to backup to my hard drive. Then making a backup of that copy to an external drive. It's when I make a backup of that external drive that it slows down incredibly slow. From what I am gathering, I can eliminate the 'previews' from the backup of the external drive as Lightroom can reconstruct them if ever need be. Does this sound correct to you? 

[Ken Nielsen]

I've got to include this question: what is the difference between 'previews' and 'presets' and can they both easily be eliminated from 'backups' of lcat data which I gather is the true backup of the catalog structure that links the entire Lightroom catalog together with the image files on disk?

[Conrad_C · Accepted solution]

What it’s processing is the file "Ken Previews.lrdata". Because the filename ends in "…Previews.lrdata", that is a cache of previews for a catalog named “Ken“ (full filename “Ken.lrcat”). There are two important things about the preview cache: It’s expendable (if it is lost, Lightroom Classic automatically rebuilds that cache anyway), and it can grow to be huge which will take over your storage and slow down backups.

…incredibly slow backup time when it gets to this... 'presets' part of the backup of the lightroom catalog. Is it necessary to include this?

By @Ken Nielsen

Note that it is not backing up a large presets file. It says it’s only scanning External Editor Presets (analyzing it for changes before backing it up). The file that the backup app says it’s actually processing (backing up) is the "Ken Previews.lrdata" file.

And in fact the "…Previews.lrdata" file in the screen shot has become absolutely massive. 753.7GB is over 3/4 of a terabyte — many times larger than the catalog file itself — so you are waiting for that extremely huge file to get backed up, and that huge file is also taking over a lot of the free space in your backup volume. At 753.7GB, that single cache file might be taking up more space than all of the other data on your Mac combined; remember that the base models of today’s Macs start at only 512GB of storage!

What to do about it (some of these have already been mentioned):

• There is nothing wrong with backing up that way, but assuming your backup software has an exclusion filter, use that filter to exclude all "…Previews.lrdata" files from backups. Again, these don’t need to be backed up because they’re just expendable caches. 
• You can also use the relatively new option in Lightroom Classic Catalog Settings / Previews called Limit Preview Cache Size. I set my preview cache size limit to 10GB.
• Or, you can do what I used to before Adobe added the Limit Preview Cache Size option: When my "…Previews.lrdata" file grew to be over 30 or 40GB, I would just delete it, because I need to keep space free on my limited MacBook Pro internal storage and I knew Lightroom Classic would start over and regenerate it anyway. 

In my case, I have the preview cache excluded from backups, and even if it was included it would only be 10GB (compared to over 750GB) because I have limited its size in Catalog Settings.

A note about the backup feature built into Lightroom Classic itself: It backs up only the catalog, not the "…Previews.lrdata" file or other associated files like presets.

[Ken Nielsen]

Thank You, And I will add that this may be the most valuable single help file ever in my years of using Lightroom. I will definitely be studying and re-reading every response here as this subject is like the backbone of Lightroom... everything else hinges on understanding this 'inner-workings' or 'structure' component of Lightroom. I think I have enough information in these responses to move ahead with understanding now. Thank you all for brightening my day and my working future with Lightroom. I would post this thread as a 'must read' for everyone that uses Lightroom! Thanks and good weekend to all of you!   - Ken

[drtonyb · Accepted solution]

@Ken Nielsen 

In addition to all other good advice from @Conrad_C and @Ian Lyons, the size of your "Ken Previews.lrdata" is ridiculously large. This suggests to me that something has gone seriously wrong here and LrC has lost track of much of its content. LrC now culls the Previews to prevent them from filling the disc, so how your Previews could get to 754GB in size doesn't make sense if everything was working properly.

As for External Editor Presets, I have no idea what that is: it's not in my ... Previews.lrdata.

The simiple solution, as @Conrad_C has provided, is to delete "Ken Previews.lrdata" and then let LrC rebuild it as necessary.

While you are at it, it might be prudent to delete "Ken Helper.lrdata" as well: LrC will recreate this when next launched. Better still, just rename it "Ken Helper-OLD.lrdata" to begin with, let LrC recreate "Ken Helper.lrdata" and check there are no problems. After running for a while without any issues, then you can delete "Len Helper-OLD.lrdata".

Do not delete or rename any of these while LrC is running. Close LrC first.

Ken.lrcat is your catalog: do not delete. Ken.lrcat-data holds your AI Masks and Generative AI Removes: don't delete this unless you want to regenerate all your AI Masks and Generative AI Removes, which could result in unwanted changes, especially for Generative AI Removes.

[Ken Nielsen]

I previously went into preferences and limited the saved backups to 3 as I thought that was all that is necessary. Lightroom now keeps reminding me that it can make more backups and I have to keep dismissing. I do not, and don't think anybody wants Lightroom to grow into a monster that takes over your computer. Wouldn't this be an area that would be reasonable to make easier to control. It seems now I need to keep track of three things: previews, and then the other two which are contained in this thread as things I need to pay particular attention to so they don't grow into huge backups I don't need. Wouldn't it be good for Adobe to review this thread and the wisdom given here just to impliment clear and easy controls together and simply explained in preferences? I vote for this to be implemented soon as it is needed. As it is now, these things are out of control unless you are amongst the most advanced users.