Installing with software RAID1 - How please?

Hi,

I want to set up an OMV box using RAID1 with 2x1TB disks.

I originally tried creating a RAID volume in BIOS (Dell OptiPlex 330). I can create the RAID volume, but it sits there waiting to be initialised. I can't do this in BIOS, and the info I've found on the machine says to do it using Windows disk management - obviously not an option here.
The hardware checker(?) saw sda, sdb, and md0, but in the disk picker for setting up RAID I was only presented with SDB.

I decided to start again, set the two as individual AHCI disks in BIOS, ran the installer, went to the RAID section of the OMV management gui, but still only get presented with SDB (I guess because SDA is in use).

How on earth do I set up a RAID1 OMV box when the only two disks the PC has are to be part of the RAID array please?

Many thanks.

Ah... Many thanks ryecoaaron.

So - If I install OMV on a single disk, then install the two that're going to be used for the datastore, and use OMV to set them up as a RAID pair, if the disk with the OMV install on it dies, how much trouble would I have bringing the pair back into a new OMV install on a replacement disk please?

And just in case that's a bit of an 'it might work' situation, could you tell me how I go about installing OMV avoiding the steps up and including partition creation please?
Or point me at the relevant documentation?

Thank you.