Although they work, and do the same, the installer CD & mdadm needs to support it. The specific appliance that I want to install, doesn't support RAID 10, so I need to install RAID 1 + RAID 0, i.e. setting 2x RAID 1 mirrors, and then stripe then in RAID0 - but once the first 1 mirrors are setup, I can't stripe them.
Aren't you using CentOS, then? You didn't tell us that... My answer was based on the assumption that you were talking about CentOS...