I know nothing about SnapRaid. But my mythbackend box is the one using mhddfs, and it works swimmingly well without me having to fuss over it all. That box has a Core2duo CPU (2X @2.6MHz), and the minimal CPU hit of mhddfs has never been the slightest issue or concern. The NFS server in the box delivers over 100MBytes/sec to other machines on the GigE LAN from the mhddfs array.

No form of RAID is a backup, and neither is mhddfs. Sure, it is far more dead-drive tolerant than any RAID, but I still recommend that everyone have at least one extra copy of their data (aka. a "backup").

Cheers