Backing up Catalog Previews.lrdata and/or Catalog.lrcat

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Ruahrc

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I am revising my backup scheme since I got a new hard disk. I use OS X BTW.

I found that backing up the file "Lightroom 2 Catalog Previews.lrdata" really slows down the process because it is large and also is a package and contains about a million folders and files in it. This really slows down my backup software as it scans through each and every one of them looking for a change.

There seem to be 2 critical files for LR2. One is this "Lightroom 2 Catalog Previews.lrdata" and the other is "Lightroom 2 Catalog.lrcat". LR2's weekly backups only seem to back up the .lrcat file.

I read somewhere that the Lightroom 2 Catalog Previews.lrdata was merely all the pre-rendered previews for your pictures, and that if it were to be damaged or lost you could reconstruct it by simply having LR reprocess the previews. Time consuming, yes, but you wouldn't have lost any critical data.

Does that mean that all the important info (picture location links, and most importantly the edit data) is all stored in the much smaller Lightroom 2 Catalog.lrcat?

If so, then I would like to exclude the previews (.lrdata file) from my backup as it will save time and HD space. And I am willing to go through the re-rendering of previews if a failure ever occurs. But I could not verify if you erased the previews catalog, your edits would still be recorded and you would nto have to do them all over again. In other words, is all the edit and adjustments data stored in the catalog (.lrcat) file and NOT in the previews file (.lrdata)?

Just want to make sure!

Also, I hear a lot about people having .xml sidecars next to their NEF files. I don't seem to have any, despite importing NEFs and making edits to them in Lighroom. Why is this?

Ruahrc
 
Yes, the .lrcat is the "Catalog". All metadata, history, collections, flags, etc, are stored in that one file. I never back up the previews because as you say, there's LOTS of files and folders and it's just not necessary. In fact, if you have LR set to delete previews after a set period (I think default is 3' days?) then if you haven't touched the image in that long it will have to regenerate the preview regardless.

To get the xmp side car files you either need to select the photo/s and "Save Metadata to Files" (Cmd/Ctrl + S) or under Catalog preferences turn on "Auto Write XMP Metadata". Backing up the xmp files that have changed is a good way to have another level of backup beyond just the catalog file... although not all catalog info is saved to the side car.
 
Jason is almost completely correct -- the main point is, right, don't bother backing up the previews.

There's one error, not particularly relevant to the original question, which is that only the 1:1 previews can be discarded automatically after a period of time. The smaller previews are retained.
 
D'oh... knew that.
 
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