I have been shocked by the amounts I have been billed in recent months, which I felt exceeded the per-TB cost advertised for Backblaze B2. I have a feeling that my backup settings are at fault, since TrueNAS lists my backup-ed container size as 329.55GB whereas Backblaze lists the bucket size as 3431.5GB. Below are my backup settings. Should I switch the transfer mode from copy to sync?
For reference, the backup is scheduled to run daily in the early hours of the morning.
Depends on what you want. Copy will copy and sync will sync 
Since TrueNAS cloud sync task don’t come with any kind of retention policy, I would use sync in combination with object lock and lifecycle rules.
You have 3.4TB backup data for 330GB of data, which means that you changed or deleted a lot of data. The same will be true, if that data is counted because of retention and lifecycle.
What kind of data are you backing up? Do you have some lifecycle or retention policy set on backblaze?
Sorry, I should’ve been clearer! I am backing up the entire pool, but the Backblaze retention policy is 30 days. Somewhat confusing how it then gets to that overall size.
Should I switch to sync and maintain the 30 day policy via B2?
right now, you have this situation:
Day0: you have file A and B and C.
Day1: you delete file C. Since you are pushing, file C will stay on backblaze FOREVER!
Day2: you change file B. It is no B2. B2 is now stored until further changes forever on backblaze. Old file B is stored until 30 days are over.
So yes, it think that you should
