I also have 2 WD640gb blacks (AALS, with 32mb cache) in RAID0 configuration. I tried several ways to install this RAID0 and get the best speeds, and it took me a while to figure it out too.
Anyway, my story pertains to the people who have Intel chipset like ICH10R or 9, and some others too.
First I created a RAID0 from the bios raid config area (enter into it via CTRL-i keys on my mobo, a Biostar TPower I45). So I created the RAID0 out of the 2 640's, and then exited. Upon installing Windows 7 x64, I got to the partition window and partitioned the 1200gb into two partitions. First time around I halved them, so 600 and 600gb. Well, I had slow random access times (plus 12ms). So then I installed Windows again, but this time made a small, 90gb OS partition, and a 1100gb data partition. Again, same random access times, over 12ms.
Then I stumbled across an article that talked about creating more than 1 VOLUME
inside the RAID bios config area. Yes, it will still be RAID0 with the same 2 drives, but you can create more than one volume
on your RAID0. It's confusing to understand at first, because I thought they were talking about partitions, but no. RAID Volumes and drive partitions are completely different things. Actually, you could create several partition on each raid volume, if you so desire.
Anyway, I created 2 raid volumes in the bios raid config area for Intel Matrix. The first volume was for the OS and I wanted it fast. In order to achieve that, you have to create the first raid volume small, like 100gb or less if you want. This is still big enough for many apps, even some games, and still have room left. Making the first volume small forces the OS files to be written to the fastest portion of the physical HDD. Therefore, you will have faster average read times. Mine went from 12.xms to 7.4ms! I'm not kidding, I just checked it again with AIDA and I am also experiencing it.
So with the remainder of your space (1100gb) in raid bios config you create a second Volume. I have both volumes set at 128k stripe as there is space enough and I read this is the native size the drive likes to work with (that last point may or not be true, but it seems to work!). This whole process of creating more than 1 volume on your raid is called 'slicing'.
After setting the 2 volumes, exit the raid config and then install Windows. You'll see 2 unpartitioned drives that represent volume 1 and 2 that you just created. Partition them, format them. The first partition (small one) is to install your OS on. The second volume can be partitioned as one big partition or several smaller ones, whatever you want.
After installing the OS, installing drivers
, installing/setting basic stuff, reboot, and then perform your benchmark. You'll see the difference.
Now, as I said, this may not apply to you as not all chipsets will allow you to slice your raid like this (this is my understanding, at least). But for those it does apply to it will make a big difference in speed for you raid0 config.
So do you see how these two scenarios are different:
1) Create RAID0 with only 1 volume. You then partition that one volume into several (or one) partition(s).
2) Create RAID0 with 2 volumes (from the raid config area) and make the first volume small (100gb or less) to force the OS to the fastest part of the drive. Then partition the two volumes to your liking.
This has been my experience