I hope some of you Mac gods can answer a question I have. I have my 2011 iMac with Mountain Lion and a 2TB External Firewire 800 drive hooked up. I use Time Machine to back-up my iMac, But I have to leave both running 24/7. I know that I can allow both to enter into sleep mode, but how will this affect Time Machine? Can I allow both iMac and external drive to sleep and not affect Time Machine? While in sleep mode, will Time Machine still work it's magic. I would really like to get some answers.