Retrospect looks at several things when it backs up files on a computer:

• Is the file in use?
• Has the file's size changed since the software began to back up the machine?
• Is the file unchanged from an earlier backup?

If any of these answers are yes, then Retrospect considers the file unusable and marks it as unrestorable.

It is our experience at digital.forest that this happens 2 out of 10 times while we are using Retrospect, and that usually there is an older copy of that file (1-2 days older) available for restore if the desired version is unavailable.