This might answer part of your question
Part of the same thread seems to point to the fact that you have a so-called fake raid.
(see earlier part of the thread)
Software raid is ok as I understand and from the limited reading I had.
The thread I quote above say the same thing.
(I use to run a raid0, software driven, with sil3112a= fake raid.)
I suggest you use mdadm (for the raid admin; it is included with mandy)
Here is the tutorial for raid 1 I was talking about
I suppose you have read the tldp raid howto.
You should be able to skip
"Compile a RAID-savvy kernel and install mdadm and hdparm."
Mandriva should be ready for that.
(plus if it is a sata drive, hdparm does not work AFAIK)
Whether you can install the OS as raid 1 directly (w/w using the bios option),
that is just using the menu driven install, I do not know.
You can certainly mark partitions as "raid type" or whatever it is called.
Sorry I cannot help more than that.