Lightroom routinely fails to backup my catalog file. I'm running LR Classic CC 7.5 release, but the issue predates this version.
My catalog is about 4.1 GB, plus the Turner_LR5_Catalog-3 Previews.lrdata folder which is about 34 GB. My catalog has 292,611 photos.
My catalog and previews are stored on my I: drive, which has 1.3 TB of available space.
I'm attempting to backup to my H: drive, which has 434 GB of available space.
I don't have any issues with folder permissions on any of my drives. I've tried backing up to I: and to E:, with the same result.
The only thing I can figure is that LR is making use of space on my C: drive for temporary files during the backup process, but I haven't been able to find anything about this in the LR help or an online search. My C: drive was down to about 260 MB while LR was in the backup process. After the backup failed, space on C: is 354 MB. Strangely, after running Windows Disk Cleanup I have even less available space on C:.
Does Lightroom always need to use space on C: while in the backup process?
Temporary files such as Lr creates during backup are usually located on the system/boot disk. Therefore, with only around 400MB available it's very likely that low disk space is the underlying issue. BTW, this behaviour isn't unique to Lightroom. Typically, you should aim have approximately 10% available space on your system/boot disk.
First off, as lan Lyons advises, where is LR storing CACHE (you will find it in preferences, I think it’s in the performance tab), make sure it is on a large drive, preferably not the boot drive. And while you are at it, purge it (before changing its location)
Second off, that button “choose different backup folder), not at a computer just now, I suspect if you click on it, you will see just where LR currently wants to place it. Is it where you thought it was? How much space?
Incidentaly, various Adobe programs use various locations, for scratch disk, cache, and files, oh, and log files . Photoshop scratch, ACR cache, LR Cache and video CACHE, Adobe Creative Cloud Desktop has at least two places to select some sort of file location, generally modifiable via preferences (well not the log files, but insignificantly small)