Can I add a HD to a RAID without reformatting the existing HD?

[jdl8422]

I have a HD in my Mac Pro that is about 80% filled. I wanted to add another HD and configure the 2 as a RAID, Can I do this without reformatting the existing drive, or loosing my 80% capacity data?

The first HD is a 1TB and im looking to add an identical HD to make a 2TB drive.

Thanks

 

[TheScavenger]

From what I am understanding you want to create a RAID 0 array. I believe you will have to reformat.