If you have your system configured to boot from a RAID volume, you may find when installing OS X 10.7 Lion that the system will give you a warning stating, "Some features of Mac OS X Lion are not supported for the disk." While you can continue the installation and get Lion running, what this warning means is the installer is not able to create a recovery partition on your hard drive, and therefore the system will not be able to run advanced disk management features that include FileVault disk encryption.
These advanced volume management features are enabled by Apple's new "corestorage" technology, which requires the recovery partition to be present on the boot drive as the first partition on the disk. Therefore, even though you can create a secondary recovery partition such as by installing Lion on a secondary drive, you will be able to boot to it as a recovery volume but still won't be able to enable FileVault.
The Lion installer cannot create the recovery partition if unique partitioning schemes or drive configurations are already present on your boot drive. For example, if there is a "Boot OS X" volume on the drive you are using (such as would be the case with a RAID volume) or an extensively partitioned volume that contains a Windows installation or other operating systems on it.
Therefore if you have a unique drive setup and are getting this message, then your options are to either continue and know that FileVault and other advanced disk management features will not be available, or to reconfigure your drives and set up Lion on a clean and freshly partitioned volume. If you plan on doing this, then you can reconfigure your drives through two routes:
Use Snow Leopard
The first way is to reconfigure your drives using an old Snow Leopard installation DVD. To do this, make sure you back up your current installation, boot to the Snow Leopard installation disk, and use Disk Utility to destroy your RAID volume, and then restore your backup to the drive. After this is done the Lion installer should be able to set up the recovery partition properly.
Use the Lion installation
You can follow a similar procedure by first creating a boot DVD from the Lion installer and then using Disk Utility after booting to that DVD to destroy the RAID and set up a fresh installation of Lion. You can then migrate your data and settings from a Time Machine backup when booting to Lion for the first time.
Note that Time Machine will not save your alternate operating system installations, so be sure to properly back them up before you repartition your drives.