I wish I knew first hand how Rockstor would work with backblaze. But 45drives can ship them with CentOS which is what Rockstor is based on.

I've had the opportunity to install Rockstor on various hp gen7 and gen8 servers and had no problems.

I witnessed Rockstor install just fine on an old Isilon node and was told that the performance was quite good -- sorry I have no specifics.