another useful info for RAID0 is the disk strorage number:

2 disk: m2.4xlarge : 1680 GiB instance storage (2 x 840 GiB)

4 disk: c1.xlarge : 1680 GiB instance storage (4 x 420 GiB)

more info:

http://docs.amazonwebservices.com/AWSEC2/latest/UserGuide/in...

and a quick start: "RAID0 ephemeral storage on AWS EC2"

http://www.gabrielweinberg.com/blog/2011/05/raid0-ephemeral-...