Right now I have a Magento backup going with a huge set of Session Cookies being backed up.  I've been waiting half an hour now to plow through them.  Expect that rebooting the server would leave a Backup in progress marker, perhaps and need to be cleared.

Alternatively killing the process, killing the backup, clearing the sessions folder and starting over without restarting....  Just saying.

I really need to just exclude the Sessions folder from Backups though.