From testing we have seen setups with problematic racks / datanodes that would not suffice basic EC usages. These are usually found out only after the tests failed.
We should provide a way to check this beforehand.
- not enough datanodes compared to EC policy's highest data+parity number
- not enough racks to satisfy BPPRackFaultTolerant
- highly uneven racks to satisfy BPPRackFaultTolerant
- highly uneven racks (so that BPP's considerLoad logic may exclude some busy nodes on the rack, resulting in #2)