if you are using raid1 then the other HDD is just a mirror of your principal hdd, so, if you have 2x 120 gigs, then both drive has the same data. RAID0 strip the data on each HDD, so if you have 2x120 gigs, then it addup a 240, so if one fail, then the whole array will fail as there is only chunk of data on the hdd.
RAID 1 is secure, because you dont care about doing a backup, it is done automatically. This, create a false safety environnement, as if something goes wrong with the PSU or with the controller and both drive fries or get corrupted, you're done anyway. RAID0 is just like having one hdd. When you get 1 hdd, you know that it may fail, or not. If you get 2, one may fail, or not. but anyway, you are making backup on media outside your computer, so even if your computer burn in flame, your valuable data is still safe. If you do backup your data and you are using raid1, then you are wasting valuable storage place.
Dont get me wrong, I know that for enterprise with server that contain valuable data, raid is useful and even necessary. but we are talking about PSU that cost as much as your whole computer here... and what about the RAID card?.
personnal and commercial are 2 different thing. So, whatever raid you choose, it is always best to have a backup of personnal data. With dvd burner and dvd media cheap as they are now, it is the best protection someone can have.
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