Why is there a huge file size difference between the LR Catalog and Preview Data Files?

[jenniferd34375531]

Hi - I have had to find alternative means to backup data since my HD is not large enough to contain all of the LR data files. My Catalog (size 1.18 GB) is still on my Mac HD,  while I have linked my Previews data file (almost 500 GB) to an external HD for storage and backup. 

My question is, why is there such a large file size descrepancy between the Catalog and Previews data files? I create 1:1 previews. 

Thanks for any input! Just want to ensure I haven't done something wonky to my catalog. 

[Theresa J]

Does your catalog contain a bunch of Smart Previews? Those are large.

[jenniferd34375531]

Yes, the previews data file contains 1:1 previews... I understand they are large. I just wasn't expecting to have such a massive difference between the catalog and the previews files. (1.18 GB vs. 500 GB) 

[JP Hess]

The reason for the difference in size is because you are creating 1:1 previews for all of your images. That means for every one of your images you are creating a full-sized preview image. If you are using the library module a lot those full-sized previews will speed up display of those images somewhat. You can save some space by generating minimal previews. I don't use the library module as much as I use the develop module, so I don't generate 1:1 previews. The develop module does not rely on the previews, but generates its own preview of the image.

[jenniferd34375531]

Thank you so much! I thought this might be the case, but it was such a large descrepancy I wanted to check with the community. Appreciate it!

[dj_paige]

Are you thinking that the catalog is 1.18GB because it contains your photos, and the Previews are so much smaller, that's a problem?

The catalog does not contain your photos. There is no relationship between size of catalog and size of previews.

[jenniferd34375531]

Ok. Please tell me what exactly the catalog contains so I'm aware. 

[richardplondon]

The Catalog contains database infrastructure and catalog organisation plus a copy of all image metadata but also I believe it contains a thumbnail bitmap of all the images imported. Certainly the more images in the library but also I would expect the more complex and 'heavy' their editing and their organisation, the larger a Catalog can be expected to get.

On the subject of 1:1 previews, an expiry period can be set after which that disk space is reclaimed.

IMO these 1:1 previews are only useful to keep ready-at-hand, for the set of images one is principally working on at that moment. Any others that you may actively return to, will thereby qualify for 1:1 previews then and their expiry counter will then reset.