Re:How big should a backup hard drive be?
1. The backup hard drive should match the size of the hard drives you want to back up. My recommendation would be to split the audio and sample onto separate internal 750GB hard drives. Doing this has the effect of reducing the read/write load put on the single 750GB hard drive you have for combined audio and samples. Next, purchase a 1.5TB to back up the two audio and sample 750GB hard drives. Then get a third 750GB hard drive to back up the OS Program drive.
2. All backup drives should be external, either USB, firewire, or eSATA.
3. Acronis True Image can create a mirror backup if you use the Clone Drive option, but this mirror is not a real-time mirror backup.
4. You might want to check out a program such as Microsoft Sync Toy to do a file level backup of your audio and samples. In a file level backup you can set it up so that only the files that have changed on your internal drives are mirrored to the external back up drive.
Rok Box MC