关于datanode多磁盘存储策略

目的:

节点内各存储磁盘均衡

相关参数：

dfs.datanode.fsdataset.volume.choosing.policy=org.apache.hadoop.hdfs.server.datanode.fsdataset.AvailableSpaceVolumeChoosingPolicy

与如下任一结合即可

dfs.datanode.available-space-volume-choosing-policy.balanced-space-threshold	10737418240	Only used when the dfs.datanode.fsdataset.volume.choosing.policy is set to org.apache.hadoop.hdfs.server.datanode.fsdataset.AvailableSpaceVolumeChoosingPolicy. This setting controls how much DN volumes are allowed to differ in terms of bytes of free disk space before they are considered imbalanced. If the free space of all the volumes are within this range of each other, the volumes will be considered balanced and block assignments will be done on a pure round robin basis.
dfs.datanode.available-space-volume-choosing-policy.balanced-space-preference-fraction	0.75f	Only used when the dfs.datanode.fsdataset.volume.choosing.policy is set to org.apache.hadoop.hdfs.server.datanode.fsdataset.AvailableSpaceVolumeChoosingPolicy. This setting controls what percentage of new block allocations will be sent to volumes with more available disk space than others. This setting should be in the range 0.0 - 1.0, though in practice 0.5 - 1.0, since there should be no reason to prefer that volumes with less available disk space receive more block allocations.