HDFS DataNode写数据选目录逻辑

callstack:

 

FsVolumeList.getNextVolume(StorageType,long)----->FsVolumeList.chooseVolume(List,long)----->RoundRobinVolumeChoosingPolicy.chooseVolumn(List,long)

 

OR

 

FsVolumeList.getNextVolume(StorageType,long)----->FsVolumeList.chooseVolume(List,long)----->AvailableSpaceVolumeChoosingPolicy.chooseVolumn(List,long)

 

 

 

 

前者： Choose volumes in round-robin order.

后者： A DN volume choosing policy which takes into account the amount of free space on each of the available volumes when considering where to assign a new replica allocation. By default this policy prefers assigning replicas to those volumes with more available free space, so as to over time balance the available space of all the volumes within a DN.

 

 

 

默认采用RoundRobinVolumeChoosingPolicy

可以通过配置dfs.datanode.fsdataset.volume.choosing.policy参数来使用AvailableSpaceVolumeChoosingPolicy策略