I know you can do the following in Linux LVM and can only assume that it may be possible on other OS's:
Use the Volume Manager to set up your redundancy and data striping for reliability and performance.
Simply use both disks as physical volumes for a LVM volume group and create a LVM logical volume with the correct redundancy and striping when setting up logical volumes.
-m, --mirrors Mirrors
Creates a mirrored logical volume with Mirrors
copies. For
example, specifying -m1 would result in a mirror with two-sides;
that is, a linear volume plus one copy.
So for example the commandline lvcreate -m1 -L 10G -n <name> <volume_group>
would create a mirrored logical volume or the equivalent of a RAID1 array.
-i, --stripes Stripes
Gives the number of stripes. This is equal to the number of
physical volumes to scatter the logical volume. When creating a
RAID 4/5/6 logical volume, the extra devices which are necessary
for parity are internally accounted for. Specifying -i3 would
use 3 devices for striped logical volumes, 4 devices for RAID
4/5, and 5 devices for RAID 6.
If you have three disks 2 would be the maximum number of stripes (the third is for parity) and lvcreate --type raid5 -i2 -L 20G -n <name> <volume_group>
would set up the equivalent of three disk RAID5 array.