FlexRAID provides the cleanest integration into WHS 2011 out of all solutions out there.

FlexRAID requires no plugin and presents its Storage Pool drive as a native NTFS drive to WHS 2011.
This means you can add and manage a FlexRAID pool drive just like a regular but massive drive in WHS 2011′s dashboard.

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Without much details, here are spoilers of the new FlexRAID Cruise Control UI.

The power of FlexRAID is trilling to advanced users but daunting to novices. Finding the perfect balance in a UI that is usable to both is non-trivial. Well, I took a stab at coming up with something that will please both groups. [...]