I rebuilt my WHS to a Win8 SS base system, migrated 20Tb of data over to it... Then, 60 days later I rebuilt it to WHS 2011 and migrated it all back again.
Win8 StorageSpaces is horrible! I had multiple SS crashes and data corruptions. In addition, what isn't really mentioned well, is the way the system works under the hood. When you build a storage pool, you're building a data set. The default setting for this data set is 3 disks. This means that it builds the parity arrays in sets of 3. So, unless you're adding disks in sets of 3, it doesn't operate the way you intend. Further, there's no way to modify this setting on an active pool, so you need to rebuild everything once you figure this out (unless you build it manually from the beginning).