IMac – What are the recovery options from an encrypted Time Machine

The Time Machine drive should be equal to or larger than the drive that it backs up. TM images the drive completely, then saves incremental changes. Time Machine saves the hourly backups for the past 24 hours, daily backups for the past month, and weekly backups for everything older than a month.

If your internal is 500GB with 100GB free (using 400GB), and your TM is 500GB, then you will get a full image, and then some amount of history (filling up the remaining 100GB of the TM disk). The history length depends on your use habits.

• Change a few small files occasionally? Lots of history.
• Change lots of big files a lot? Then the 100GB free will save a few hours or days.

If you have a bigger TM, you will have a longer history to browse.

I personally have a mostly full internal, an equal sized TM, and change files quite often, and find that I usually have a few months of history. Plenty of time to restore a file I accidentally delete.

To answer your first question about the keychain and whether you should encrypt backups: the passwords in your keychain are already encrypted, that's why you always have to type a password (by default your login password) to show stored passwords. So there's no immediate need to encrypt.

Of course, you could add Time Machine encryption to provide a further layer of security. This is possible starting with OS X Lion and Mountain Lion (from http://support.apple.com/kb/ht1427):

OS X Lion and Mountain Lion let you encrypt the Time Machine backup external drive using FileVault 2.

FileVault2 also uses your login password, though. So if the bad guys are able to guess or crack that password, they will have also access to your keychain information. Choosing different passwords for login and for accessing your keychain would protect the keychain passwords in such an event.

Either way, use strong passwords, password quality is of foremost importance to protect your data.

EDIT:

The OP asked in a comment how to set different passwords for login and keychain. Here is how:

• Open Utilities>Keychain Access.

• Right click each keychain and select 'Change Password for Keychain XYZ':

  

If you prefer to use your current password as keychain password and change your login password, log in using another account and change your account's password from System Preferences>Users & Groups. That will only change your login password, not your keychain password.