RAID 0 setup does not contain full disk space from slices I just setup a striped RAID 0 on my 2012 MacBook Pro with two SSDs.  One drive is 256 GB and the other is 500 GB, but my RAID disk is only 510 GB.  Disk2 is my RAID disk, with disk0 and disk1 being slices.

Does anyone know what's going on and how to fix this?  

I erased all disks prior to setting this up.  See attached image from diskutil list output.

I used the OS X Yosemite Disk Utility to setup the RAID and now I am running El Capitan.
You can't fix this. The size of a RAID is always a multiple of the smallest volume used in the setup.

The chunk sizes (stripe sizes, interlace sizes) as well as the number of chunks have to be equal on all used volumes. Usually the chunk size is 64 kb. These requirements are determined by the size of the smallest disk and limit the size of the resulting RAID volume.