|Are you certain you have it set up as RAID 0 ? |
And why would you do this? You do realize that in a RAID 0 configuration if you have any problem with either disk you will lose all info off both disks.
With large drive capacities there is no valid reason to use a RAID 0 configuration. There is a perception that this will give greater speed but the difference is negligible and the risk of loss is magnified. If you need a single partition of 1TB capacity ( and why would you anyway) why not just buy a 1TB disk?
arranging the two 500mb drives in a mirrored array instead of spanned makes a lot more sense. Automatic redundant backup if ( when) a disk develops a problem.
Goin' Fishin' (Some day)