backupencryptionhfs+time-machine
I formatted one partition on my external drive as MacOS Extended (Journaled, Encrypted).
Now when I open Time Machine and want to use that partition I see a checkbox Encrypt backups.
Because I don't want to encrypt my backups twice I unticked this checkbox. But when I continue Time Machine asks me for the password of this partition to be able to turn off the encryption.
I do not want to turn it off.
How can I use already encrypted disk?
No, the backups will not be encrypted automatically, but it's very easy to enable for directly attached disks. Just check "Encrypt Backup Disk" in the Time Machine disk selection settings.
If you're backing up to another Mac, you can use Disk Utility on that Mac to erase non-boot drives and put an encrypted partition on them:
I deleted the old backup and created a new one, with encryption on:
Yes, the checkbox in the above screenshot is displayed as checked if the backup is encrypted.
Best Answer
This unbelievable problem has simple solution. Just leave the checkbox ticked and the encrypted partition will be used as is. No double encryption.
If you check the help ? there is written that the disk does not support encryption if the checkbox (Encrypt backups) is dimmed. Hence implying Time Machine is using disk encryption not another one on top of that.
So the checkbox is just for people who had not prepared the disk yet.