Do i need an operating system on a backup hard drive

You don't need an OS if you're just backing up data; just do it like above.

Since they're internal drives, if they're the same size and speed, you may be better off just setting up a RAID1 array. Then they will automatically mirror each other - the OS, programs, files, everything will be identical. So if one goes bad, you have a complete, running copy of your entire machine, not just the data. Another plus is that it creates the mirror automatically in real time, so you literally never have to worry about doing anything.
 
No. It's a drive like any other drive. A local internal drive as a backuo only works as ling as the drive works, If your computer gets hit by a power surge, lightning, fire, or something else, there's no guarantee that the drive will still work.

Raid 1 is not a true backup, it's a redundancy against a HDD failure. It won't protect against deletion, corruption, or provide any historical versions of any files. Even with raid you still need a backup

Think about an external backup drive that can be kept somewhere else(possibly even off-site) when not in use. Many people did this with Zip drives in the 90's, but now external drives are popular.

 


This is definitely good advice, and something I do even with a RAID array. He should think about it this way: What if the computer is stolen, or your whole house gets flooded? That's why an internal backup still leaves you at risk. But if I was going to do one anyway, I'd sooner just go with RAID1 and be done with it, since you need a second method anyway, and RAID1 will at least save you a pain in the neck if one of the drives goes bad.

An internal non-RAID backup just gets you the worst of both worlds.