1. File was written to DN1, DN2 with RF=2
2. File stream opened to read and kept. Block Locations are [DN1,DN2]
3. One of the replica (DN2) moved to another datanode (DN3) due to datanode dead/balancing/etc.
4. Latest block locations in NameNode will be DN1 and DN3 in the 'same order'
5. DN1 went down, but not yet detected as dead in NameNode.
6. Client start reading using positional read api "read(pos, buf, offset, length)"