Please help review HDFS-6009: tools for datanode-level io isolation

[Yu Li <ca...@gmail.com>]

Dear all,

In our product env we find a need to do some datanode-level io isolation,
and worked out a solution using favored node(HDFS-2576). Simply speaking,
we arrange logical datanode group for different applications and make each
application only write data to the relative datanode group, so failure of
one datanode will only affect one single application.

HDFS-6009 is an umbrella for supplying a bunch of tools after datanodes are
grouped, such as balancer within a group, and check and bring cross-group
placed block back (favored node cannot control data replication in case of
datanode failure). I've uploaded the patch for HDFS-6010, and patches for
HDFS-6011/6012 are ready but depends on some new class introduced by
HDFS-6010, so will upload them later.

I'd really appreciate it if anyone could share his opinion on whether we
need these tools in hdfs, or help review patch of HDFS-6010. Thanks.

-- 
Best Regards,
Yu Li