1. Spanning is not to be confused with striping. Spanning is only useful when dealing with extremely large files, such as uncompressed video and, unlike striping (RAID 0) it does not add any performance gain. 2. It's possible to combine the benefit of striping with the benefit of mirroring, by choosing RAID 1+0 (RAID 10) but it requires at least four harddisks and all four have to be attached to the same RAID controller. Windows 7 software mirroring does not suffer from these limitations. It can run on top of a normal RAID 0 array also, like I said. Another benefit of Windows 7 software mirroring is it allows you to decide which portions of your harddisks will be used (the innermost, slower performing zones versus the outermost, faster performing ones). Also, if more than one controller is used for mirroring (this is called duplexing) then if only one of both controllers fails, the other one continues to function normally. However, since the Intel ICH10R controller is built into the chipset of the motherboard I, personally, would not worry too much about it potentially failing. That is, not unless it's a Sandy Bridge rev. B2 chipset, which has the design flaw they discovered in February.