As a side effect of the drive pooling being removed in WHS2011, a lot of 3rd party utilities cropped up to fill the gap, some of them quite good, like DriveBender, FlexRAID, and StableBit DrivePool.
I am now using StableBit DrivePool, and am quite happy with it. It stores whole files on NTFS volumes like the old WHS, with the same directory structure as the logical pooled drive, just in a hidden folder. So if you have 4 drives with a replication setting of 2, you might have 1 file duplicated on drives 1 and 2, another file duplicated on 3 and 4, another on 2 and 3, etc. So if your server were to crash, the drives could be popped in another machine and folders copied out & merged from each drive easily. The duplication level can be adjusted on a per-directory basis (for example I turned off duplication on the live TV buffer directory and syncron temp directory).
I removed the drive letters from the drives being used for the pool, and it runs fine like this, including nightly defrag.
I've seen mostly negative reviews of Storage Spaces performance -- the performance of DrivePool is quite impressive, especially with the recent feature to stripe reads across drives for a single mirrored file. I have seen files get read and scanned for commercials on my whole-home DVR at over 150MB/s, using 4 WD Red 4TB drives with a duplication level of 2, for an effective 8TB capacity. Decompressing large archives of tiny files in the pool is ridiculously fast. The only time I've seen the pool performance not be SSD-like is when opening a directory with over 1500 files in explorer and waiting for it to change the sort or update all the icons.
You can get the StableBit Scanner bundled with Drivepool, and it is a pretty nice SMART monitor and background scanner for bad clusters, with the ability to e-mail/page you if it looks like a drive needs replacing soon. This will tell you the serial number of the failed drive, so it is easy to identify even when you have a bunch of identical drives in the pool.
The only downside I see with DrivePool is that hard links and junctions are not currently supported, and that there is no option for parity drive(s) instead of mirroring. (Flexible parity seems to be the forte of FlexRAID). I think the mirroring will end up with far better write performance than parity though.