How does Backblaze handle large files?

By default Backblaze does not have any file size restrictions:

The Backblaze software uploads files sequentially from smallest to largest. This allows the smallest files on each system to be uploaded in batches, significantly improving upload rates due to reductions in overhead. 

Files that are larger than 100 MB are parsed into 10 MB chunks for transmission. 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, and the next file is processed

If you have an external drive, you can set a "temporary data drive" in the Backblaze settings to one of your external drives with ample space. This means that when that external is connected and available, Backblaze will set its temporary folder to that external drive, and perform its chunking operations on there - avoiding your internal drive. The only time it'd use the internal drive is if the external is unavailable.

Versioning of large files is limited to one every 48 hours. So, if a large file is changed multiple times throughout a several day period, only 1 version of that file will be uploaded every 48 hours. 

If you have extremely large files that are slowing down or clogging your backup, you may want to consider excluding the large files from backup.