Whether it comes setup or you have to do it yourself depends on the vendor. Some vendors will setup RAID and install the OS on it for you, others won't, I'm sure.
Ayasin was completely correct about the aspects of RAID 0. With hardware RAID-0, such as supported by the 8890, operation is completely transparent to software, the software only sees one large, high-speed disk. So installing the OS on it is no propblem.
The equivalent statistics to what Ayasin gave, but for RAID-1:
- A drive that appears to have the same capacity as the smallest drive in the array. So if you have a 40 GB and a 60 GB drive in the array, you'll have what appears to be a 40 GB drive and 20 GB of lost space. (That 40 GB is mirrored, so occupies another 40 GB, bringing the total to 100, the combined capacity of the drives).
- A drive that, on writing, appears slightly slower than the slowest drive in the array.
- A drive that, on reading, appears slightly slower than the fastest drive in the array. (Assuming the controller is smart enough to pull the fastest copy. RAID-1 has no way to determine which copy contains errors in case of discrepancy, so there's no reason to compare the data to what's on the slower drive).
If you use two identical drives, a RAID-1 configuration looks to software like a single one of those drives.