I have an LR catalogue with about 65k images on my Mac Pro, which is backed up to a Sonnet box stood next to it using Chronosync
I'm now trying to create off site backup of just my best images. So I set the filter to show only images with 3+ stars, which is about 3,500 pictures.
I thought the easiest way would be to export these 3.5k images as a catalogue - that way I maintain the develop settings, folder hierarchy, collection structure etc of all the pictures.
So I select all 3.5k images and choose File / Export as Catalogue... and I select "include Negative Files" as I need the original raw files too.
The operation appears to complete after about 15 minutes, but then informs me that about 700 of the images were not copied to the new location!! There is plenty of space on the other drive, so why is this not working properly?
I had some free time and decided to perform some tests on my Mac Pro. I selected 6k images (RAW Canon CR2 and Nikon NEFs). I checked negative files but unchecked previews. The export was fast but Lightroom (version 4.2 running on Mac OS X 10.8.2 - export on a freshly erased 1 TB drive) displayed a message indicating that 1140 files hadn't been copied.
I tried a second time with only 3800 files and everything went smoothly.
I tried a third time, with 5800 files and the export finished with any mention of "not copied" or missing files.Edit
: I tested a fourth time. This time, I quit Lightroom and relaunched it. I selected 7.5k files and exported as catalog. Surprisingly, everything went fine and I checked that no file was missing in the exported catalog.