A Stupid question:
2 x 40GB SSD meaning I can have all the 80GB disk size?
Or only 40GB, one for RAID
The disk is provided to you as raw block devices, which you can configure however you'd like. I'm presuming you're talking about instance storage here, correct? Not EBS? If indeed your are talking about the local instance storage, you need to know that data stored on those disks go away whenever your server gets shut down (either voluntarily or involuntarily).