To avoid duplicating data, Backblaze will not back up any drive that contains Time Machine data on it. The drive will be listed in Backblaze's "Select Hard Drives to Backup" as Time Machine and will not be selectable.
If you'd like to back up that drive to Backblaze, you can discontinue using Time Machine, delete its backups, and select it for backup to Backblaze. Before following these steps, make sure you do not have any data you need to restore from Time Machine as it will be entirely deleted.
After following this article, you can turn back on Time Machine and point it to a completely different drive that you're dedicating solely to Time Machine if you'd like. Backblaze can coexist with Time Machine, however you can't back up the contents of a Time Machine drive to Backblaze.
1. Turn off Time Machine
Open the System Preferences and choose Time Machine. Turn Time Machine off.
2. Delete Backups.backupdb from the Time Machine drive.
You may be prompted for your Mac OS X administrator password. This folder may contain a lot of files, and take a long time to move to the trash, and to empty the trash.
Note: This step will delete your Time Machine data.
3. Select the drive in Backblaze's settings
Open the System Preferences, choose Backblaze and click on Settings.
Select the drive for backup to Backblaze.
Click OK to accept the changes.