I just bought a Western Digital 4TB My Book Studio Edition II Quad Interface External Hard Drive for use with my relatively new iMac. I plan to keep all my video on this drive, and nothing else.
It comes with RAID 1 (I can't tell whether it automatically runs it, or whether I have to choose running it as an option. I also can't tell whether the 4TB capacity is calculated after it is running or not.)
I know RAID is not a back-up, so whether I use it or not, I'll need to back up my video files.
Question 1 is: if RAID 1 is optional, should I use it for added data security.
Question 2 is: what is the best method to back up the data: backing up on the same drive, or backing up to another external drive.
Question 2a: If it is best to back up to another external drive, how much capacity will I need, assuming I won't ever put more than 3 TB on this 4TB drive?
If you've got a separate backup of the data (an excellent plan), then you ONLY need RAID-1 if you're concerned about down time. RAID-1 will save you from having to wait to restore your data if a drive fails. Unless you're serving video files to other people, or if you're using this for scheduled video recording and you'd get really p*ssed off if your system didn't record a show, I'd guess that downtime isn't that big an issue for you.
You do NOT want to back up the data to the same drive. If the drive dies then you've lost the original AND the backup - that kind of defeats the purpose of the backup.
You need an external drive large enough to hold the files you plan to back up. If you plan to back up 3TB of files, you need a drive large enough to hold 3TB.