[TiredOfLife]

Storage Spaces doesn't dedicate drive to single purpose. It operates in chunks (256MB i think). So one drive can, at the same time, be part of a mirror and raid-5 and raid-0. This allows fully using drives with various sizes. And choosing to remove drive will cause it to redistribute the chunks to other available drives, without going offline.

[cm2187]

And as a user it seems to me to be the most elegant design. The quality of the implementation (parity write performance in particular) is another matter.