Bluephoton
The idea is that you install the sme OS with the main drives only in place ie 2 x 500Gb to make a RAID1 array.
After install is complete etc, you then power down and add the additional drives as per the Howto, and I would suggest one at a time to avoid potential multiple issues/errors at the same time.
The only "no raid" command that is supported is at initial sme OS installation time where you can issue a switch to tell sme NOT to configure a single drive as a RAID member (in degraded mode), where the server only has one connected drive.
The default single drive install configures the drive as a degraded RAID1 member, which sme will run with perfectly OK, and this allows you to easily add a second drive to the RAID1 array later.