To ensure that all drives correctly update you must make sure to keep your drives plugged in simultaneously as much as possible.
If you have multiple external hard drives, you will first want to make sure that each is correctly selected:
1. Open Backblaze Preferences (Mac) or Backblaze Control Panel
2. Click 'settings'
3. Check the boxes next to the drives you want to select for backup
If any drives are showing as 'unplugged', please follow this link.
Once your drives are all selected, you will want to make sure to keep your drives plugged in simultaneously as much as possible. Our system has a way of updating your drives, even if there is nothing remaining to upload. In order for this process to work, you must have all of your external drives plugged in simultaneously. You must also make sure that only the drives you need backed up are selected in the (as shown in the screenshot above).
Once you've made sure that all your drives are plugged into your computer at the same time and that they are selected for back up you can force the rescan by holding down the ALT/Option key and clicking the "Restore Options..." button on the Backblaze control panel.
If you continue to see your drives not update, please contact support.