I'm just started using time machine so I'm not that familiar with it. After about a week I started getting an error that my drive is full and it can't back up anymore. But when I check there's almost 170GB free (on a finder level) but 24GB within the time machine preferences. I thought time machine deleted old backups as it goes? I'm running 10.8.5 on a MacPro3,1, using a 1TB time machine drive. There's about a dozen or so successful backups so far.