Multipack :
Yes you effectively halved the peformance if they are all the same speed disks, as RAID 0 uses the two disks speeds at once, but you havent compromised any data and can be safe in the knowledge that you arent going to lose any of it. It's always a good idea to backup RAID 0 arrays regularly anyway!
Thanks for your response and sorry for not explaining myself correctly. What I'm wondering is: By cloning a RAID0 to single HD, did I lose performance compared to if I formatted the new HD (no RAID) and transferred the information from RAID0?. I've found that now, if I change my BIOS configuration to stop using RAID, the new drive just doesn't boot, and that makes me question about the internal format of the new drive...