Why do I get a popup saying "NOTE: Your Computer Is Low On Disk Space"?

Backblaze backs up individual files to an unlimited size by default (this can be reduced in the Backblaze Settings). If your computer's system hard drive has less than 1.1 times the size of the largest file scheduled to be backed up left in free space, Backblaze will not back up that file and alert the user. To enable these files to be backed up, please free up enough space on your computer for 1.1 times the size of your largest single file.

The reason Backblaze needs 1.1x the largest file is how it backs up. Here's the process: 
• Let's say you have a 10 GB video file that needs to be backed up 
• The file will be copied in 10 MB chunks to a temporary Backblaze folder (that's 1x the space of the file) 
• Each chunk will be checksummed, packaged and prepared for transfer (that's up to 0.1x the space of the original file, but typically less) 
• Each chunk is transmitted 
• Once all pieces are transmitted and confirmation is received from the servers, the chunks are deleted from the temporary Backblaze folder, and the next file is processed

Alternately, a Temporary Data Drive is available in the Backblaze settings. If you have a secondary drive with more free space than your boot drive, you can set Backblaze to write to that drive rather than your boot drive.