My guess is you've read the faq and are still confused as to how having both active helps in any way. The answer is, it doesn't. In fact, depending on your HD controller(s) it can be slower than plain RAID 0. The advantage, however, is that you also get the redundancy of RAID1. As a simple example, let's take a 2-disc RAID0. Because the data is split up over two disks, it can be written (approx) twice as fast. A 512k file, for example, will be written at the speed of a 256k file because both HDs work simulataneously. However, if either disk fails, all of your data is lost. Not good. Now take a 2-disc RAID1. Speeds will be approx. the same as a single, non-RAID drive, but both disks would have to die before you lost any data.
Now combine the two:
A 512k file is split into two 256k parts. Each of these parts gets written to two drives, all at the same time. Plus, if any one drive fails, you've already duplicated all the data on a spare HD which will kick-in on the fly, causing 0 downtime and 0 lost data. The key to RAID is that multiple HDs can be working simulataneously, giving the appearance of reduced write-times. This is one reason why RAID works better on SCSI than on IDE, but even that is changing as IDE buses become faster and faster.
