The other day I got a new backup HDD so I can rotate my external disks and take them offsite in case my house blows up. I enjoy disk encryption on these sorts of drives that will be stored safely and the data is inaccessible. However, after backing up my data I realized that I didn't employ ZFS encryption on the drive! Am I going to have to nuke the data on my external drive, recreate the dataset and enable encryption, or is there a way to encrypt existing data? What would you suggest?