I'm backing up with Time Machine on a Mac Pro to an internal hard drive. I have encrypted my Time Machine backup in system preferences. This resulted in an initial backup of about 2 days, and backups are now slower than they were when unencrypted. A glance at the Time Machine menu bar item often shows the status "Encrypting Backup Disk... (X %)" Presumably it is encrypting more space to allow for the impending backup as the entire drive isn't pre-encrypted.
I have encrypted other internal drives by right clicking and choosing encrypt. It seems that wiping my Time Machine hard drive, encrypting the drive and then doing non encrypted Time Machine backups would protect the data just as well, and offer faster backups. Would encrypting the drive itself prevent restoring from the backup or are there any other drawbacks?