Source : XLR8yourMacWe first faced this problem when installing Leopard on a Raptor-based RAID0 volume. This issue was then confirmed by other users worldwide: it can be difficult to install Leopard on software-based RAID volume created with Tiger. The system will not boot; and you will have to press "Alt" key during booting procedure to select the RAID volume. It remains unclear why it affects only some users.
The only way to proceed is to stop the Tiger-created RAID volume then to create a new one from Leopard, however, it implies to erase all data available on RAID HDs. Of course, this was not an issue for us, as we had cloned our system on an external drive. As we already mentioned it, perform a data backup or a clone your entire system before installing Leopard.
[translation by Linathael]
