hadoop如果一个节点内有新增磁盘或者数据出现在磁盘上不均衡时，需要做磁盘均衡，就是将其他已经写入数据的磁盘均衡到新增加的磁盘上去，大概分为以下三个步骤，计划，执行，查询：

一般默认都开启了磁盘均衡，但是我这种状况特殊，公司给的初始磁盘大小不一样。。。我也没辙。。我只是试验下，我这种情况能否做数据的分散。
看下图，disk10已经91%了，剩余空间88G，但是从磁盘存储的数据来看，还是比较均衡的。。

hdfs diskbalancer -plan 
hdfs diskbalancer -execute 'plan_json_path'
hdfs diskbalancer -query 

生成计划：

hdfs diskbalancer -plan cdh192-22

plan.json

[hadoop@cdh192-22 ~]$ hdfs dfs -cat /system/diskbalancer/2022-Nov-17-10-21-45/cdh192-22.plan.json
{"volumeSetPlans":[{"@class":"org.apache.hadoop.hdfs.server.diskbalancer.planner.MoveStep","sourceVolume":{"path":"/dfs/data10/","capacity":999716507648,"storageType":"DISK","used":518103326696,"reserved":0,"uuid":"DS-4ea78bac-85e4-4d7a-92f6-72d02502e30f","failed":false,"volumeDataDensity":-0.0534,"skip":false,"transient":false,"readOnly":false},"destinationVolume":{"path":"/dfs/data7/","capacity":2399304445952,"storageType":"DISK","used":1115196706478,"reserved":0,"uuid":"DS-40172040-5a50-4f68-8201-208237f26d11","failed":false,"volumeDataDensity":9.999999999998899E-5,"skip":false,"transient":false,"readOnly":false},"idealStorage":0.4648,"bytesToMove":338470576696,"volumeSetID":"9bbee851-9964-4d91-8a61-41ae86901e37"},{"@class":"org.apache.hadoop.hdfs.server.diskbalancer.planner.MoveStep","sourceVolume":{"path":"/dfs/data11/","capacity":999716507648,"storageType":"DISK","used":464668232754,"reserved":0,"uuid":"DS-90f7fe25-1933-4167-8c14-2a9e2a143d0f","failed":false,"volumeDataDensity":9.999999999998899E-5,"skip":false,"transient":false,"readOnly":false},"destinationVolume":{"path":"/dfs/data4/","capacity":2399304445952,"storageType":"DISK","used":1115196706478,"reserved":0,"uuid":"DS-b0cd02a7-2bf7-4457-abe9-14edd486d28e","failed":false,"volumeDataDensity":9.999999999998899E-5,"skip":false,"transient":false,"readOnly":false},"idealStorage":0.4648,"bytesToMove":259615596345,"volumeSetID":"9bbee851-9964-4d91-8a61-41ae86901e37"},{"@class":"org.apache.hadoop.hdfs.server.diskbalancer.planner.MoveStep","sourceVolume":{"path":"/dfs/data8/","capacity":999716507648,"storageType":"DISK","used":464668232754,"reserved":0,"uuid":"DS-176d5992-75bd-4767-9366-93df8a0fd159","failed":false,"volumeDataDensity":9.999999999998899E-5,"skip":false,"transient":false,"readOnly":false},"destinationVolume":{"path":"/dfs/data3/","capacity":2399304445952,"storageType":"DISK","used":1115196706478,"reserved":0,"uuid":"DS-35e8ab71-a899-4ef7-be3f-d9c1f1c1561b","failed":false,"volumeDataDensity":9.999999999998899E-5,"skip":false,"transient":false,"readOnly":false},"idealStorage":0.4648,"bytesToMove":243296795330,"volumeSetID":"9bbee851-9964-4d91-8a61-41ae86901e37"},{"@class":"org.apache.hadoop.hdfs.server.diskbalancer.planner.MoveStep","sourceVolume":{"path":"/dfs/data9/","capacity":999716507648,"storageType":"DISK","used":464668232754,"reserved":0,"uuid":"DS-8b22a280-09ff-4f41-ae0a-55eaa62d300e","failed":false,"volumeDataDensity":9.999999999998899E-5,"skip":false,"transient":false,"readOnly":false},"destinationVolume":{"path":"/dfs/data6/","capacity":2399304445952,"storageType":"DISK","used":1115196706478,"reserved":0,"uuid":"DS-5179da53-7b07-465e-b07e-b4a8795c85ce","failed":false,"volumeDataDensity":9.999999999998899E-5,"skip":false,"transient":false,"readOnly":false},"idealStorage":0.4648,"bytesToMove":190630379536,"volumeSetID":"9bbee851-9964-4d91-8a61-41ae86901e37"},{"@class":"org.apache.hadoop.hdfs.server.diskbalancer.planner.MoveStep","sourceVolume":{"path":"/dfs/data9/","capacity":999716507648,"storageType":"DISK","used":464668232754,"reserved":0,"uuid":"DS-8b22a280-09ff-4f41-ae0a-55eaa62d300e","failed":false,"volumeDataDensity":9.999999999998899E-5,"skip":false,"transient":false,"readOnly":false},"destinationVolume":{"path":"/dfs/data2/","capacity":2399304445952,"storageType":"DISK","used":1107097449681,"reserved":0,"uuid":"DS-ad4ad5f7-4bc5-4cfd-80cb-cff8c6b837ca","failed":false,"volumeDataDensity":0.003400000000000014,"skip":false,"transient":false,"readOnly":false},"idealStorage":0.4648,"bytesToMove":181871783815,"volumeSetID":"9bbee851-9964-4d91-8a61-41ae86901e37"},{"@class":"org.apache.hadoop.hdfs.server.diskbalancer.planner.MoveStep","sourceVolume":{"path":"/dfs/data8/","capacity":999716507648,"storageType":"DISK","used":464668232754,"reserved":0,"uuid":"DS-176d5992-75bd-4767-9366-93df8a0fd159","failed":false,"volumeDataDensity":9.999999999998899E-5,"skip":false,"transient":false,"readOnly":false},"destinationVolume":{"path":"/dfs/data5/","capacity":2399304445952,"storageType":"DISK","used":1115196706478,"reserved":0,"uuid":"DS-183b713c-f95d-45f5-8f1e-530ea8a15ec1","failed":false,"volumeDataDensity":9.999999999998899E-5,"skip":false,"transient":false,"readOnly":false},"idealStorage":0.4648,"bytesToMove":141152455299,"volumeSetID":"9bbee851-9964-4d91-8a61-41ae86901e37"},{"@class":"org.apache.hadoop.hdfs.server.diskbalancer.planner.MoveStep","sourceVolume":{"path":"/dfs/data11/","capacity":999716507648,"storageType":"DISK","used":464668232754,"reserved":0,"uuid":"DS-90f7fe25-1933-4167-8c14-2a9e2a143d0f","failed":false,"volumeDataDensity":9.999999999998899E-5,"skip":false,"transient":false,"readOnly":false},"destinationVolume":{"path":"/dfs/data1/","capacity":2399304445952,"storageType":"DISK","used":1070758333399,"reserved":0,"uuid":"DS-ccc089fe-bb80-40d5-983e-fe678e7607b3","failed":false,"volumeDataDensity":0.018600000000000005,"skip":false,"transient":false,"readOnly":false},"idealStorage":0.4648,"bytesToMove":140740287938,"volumeSetID":"9bbee851-9964-4d91-8a61-41ae86901e37"},{"@class":"org.apache.hadoop.hdfs.server.diskbalancer.planner.MoveStep","sourceVolume":{"path":"/dfs/data10/","capacity":999716507648,"storageType":"DISK","used":518103326696,"reserved":0,"uuid":"DS-4ea78bac-85e4-4d7a-92f6-72d02502e30f","failed":false,"volumeDataDensity":-0.0534,"skip":false,"transient":false,"readOnly":false},"destinationVolume":{"path":"/dfs/data5/","capacity":2399304445952,"storageType":"DISK","used":1115196706478,"reserved":0,"uuid":"DS-183b713c-f95d-45f5-8f1e-530ea8a15ec1","failed":false,"volumeDataDensity":9.999999999998899E-5,"skip":false,"transient":false,"readOnly":false},"idealStorage":0.4648,"bytesToMove":47840136002,"volumeSetID":"9bbee851-9964-4d91-8a61-41ae86901e37"}],"nodeName":"cdh192-22","nodeUUID":"13584e04-9fdd-468b-96da-59e6be03259b","port":9867,"timeStamp":1668651705345}

json格式化后

{"volumeSetPlans":[{"@class":"org.apache.hadoop.hdfs.server.diskbalancer.planner.MoveStep","sourceVolume":{"path":"/dfs/data10/","capacity":999716507648,"storageType":"DISK","used":518103326696,"reserved":0,"uuid":"DS-4ea78bac-85e4-4d7a-92f6-72d02502e30f","failed":false,"volumeDataDensity":-0.0534,"skip":false,"transient":false,"readOnly":false},"destinationVolume":{"path":"/dfs/data7/","capacity":2399304445952,"storageType":"DISK","used":1115196706478,"reserved":0,"uuid":"DS-40172040-5a50-4f68-8201-208237f26d11","failed":false,"volumeDataDensity":0.00009999999999998899,"skip":false,"transient":false,"readOnly":false},"idealStorage":0.4648,"bytesToMove":338470576696,"volumeSetID":"9bbee851-9964-4d91-8a61-41ae86901e37"},{"@class":"org.apache.hadoop.hdfs.server.diskbalancer.planner.MoveStep","sourceVolume":{"path":"/dfs/data11/","capacity":999716507648,"storageType":"DISK","used":464668232754,"reserved":0,"uuid":"DS-90f7fe25-1933-4167-8c14-2a9e2a143d0f","failed":false,"volumeDataDensity":0.00009999999999998899,"skip":false,"transient":false,"readOnly":false},"destinationVolume":{"path":"/dfs/data4/","capacity":2399304445952,"storageType":"DISK","used":1115196706478,"reserved":0,"uuid":"DS-b0cd02a7-2bf7-4457-abe9-14edd486d28e","failed":false,"volumeDataDensity":0.00009999999999998899,"skip":false,"transient":false,"readOnly":false},"idealStorage":0.4648,"bytesToMove":259615596345,"volumeSetID":"9bbee851-9964-4d91-8a61-41ae86901e37"},{"@class":"org.apache.hadoop.hdfs.server.diskbalancer.planner.MoveStep","sourceVolume":{"path":"/dfs/data8/","capacity":999716507648,"storageType":"DISK","used":464668232754,"reserved":0,"uuid":"DS-176d5992-75bd-4767-9366-93df8a0fd159","failed":false,"volumeDataDensity":0.00009999999999998899,"skip":false,"transient":false,"readOnly":false},"destinationVolume":{"path":"/dfs/data3/","capacity":2399304445952,"storageType":"DISK","used":1115196706478,"reserved":0,"uuid":"DS-35e8ab71-a899-4ef7-be3f-d9c1f1c1561b","failed":false,"volumeDataDensity":0.00009999999999998899,"skip":false,"transient":false,"readOnly":false},"idealStorage":0.4648,"bytesToMove":243296795330,"volumeSetID":"9bbee851-9964-4d91-8a61-41ae86901e37"},{"@class":"org.apache.hadoop.hdfs.server.diskbalancer.planner.MoveStep","sourceVolume":{"path":"/dfs/data9/","capacity":999716507648,"storageType":"DISK","used":464668232754,"reserved":0,"uuid":"DS-8b22a280-09ff-4f41-ae0a-55eaa62d300e","failed":false,"volumeDataDensity":0.00009999999999998899,"skip":false,"transient":false,"readOnly":false},"destinationVolume":{"path":"/dfs/data6/","capacity":2399304445952,"storageType":"DISK","used":1115196706478,"reserved":0,"uuid":"DS-5179da53-7b07-465e-b07e-b4a8795c85ce","failed":false,"volumeDataDensity":0.00009999999999998899,"skip":false,"transient":false,"readOnly":false},"idealStorage":0.4648,"bytesToMove":190630379536,"volumeSetID":"9bbee851-9964-4d91-8a61-41ae86901e37"},{"@class":"org.apache.hadoop.hdfs.server.diskbalancer.planner.MoveStep","sourceVolume":{"path":"/dfs/data9/","capacity":999716507648,"storageType":"DISK","used":464668232754,"reserved":0,"uuid":"DS-8b22a280-09ff-4f41-ae0a-55eaa62d300e","failed":false,"volumeDataDensity":0.00009999999999998899,"skip":false,"transient":false,"readOnly":false},"destinationVolume":{"path":"/dfs/data2/","capacity":2399304445952,"storageType":"DISK","used":1107097449681,"reserved":0,"uuid":"DS-ad4ad5f7-4bc5-4cfd-80cb-cff8c6b837ca","failed":false,"volumeDataDensity":0.003400000000000014,"skip":false,"transient":false,"readOnly":false},"idealStorage":0.4648,"bytesToMove":181871783815,"volumeSetID":"9bbee851-9964-4d91-8a61-41ae86901e37"},{"@class":"org.apache.hadoop.hdfs.server.diskbalancer.planner.MoveStep","sourceVolume":{"path":"/dfs/data8/","capacity":999716507648,"storageType":"DISK","used":464668232754,"reserved":0,"uuid":"DS-176d5992-75bd-4767-9366-93df8a0fd159","failed":false,"volumeDataDensity":0.00009999999999998899,"skip":false,"transient":false,"readOnly":false},"destinationVolume":{"path":"/dfs/data5/","capacity":2399304445952,"storageType":"DISK","used":1115196706478,"reserved":0,"uuid":"DS-183b713c-f95d-45f5-8f1e-530ea8a15ec1","failed":false,"volumeDataDensity":0.00009999999999998899,"skip":false,"transient":false,"readOnly":false},"idealStorage":0.4648,"bytesToMove":141152455299,"volumeSetID":"9bbee851-9964-4d91-8a61-41ae86901e37"},{"@class":"org.apache.hadoop.hdfs.server.diskbalancer.planner.MoveStep","sourceVolume":{"path":"/dfs/data11/","capacity":999716507648,"storageType":"DISK","used":464668232754,"reserved":0,"uuid":"DS-90f7fe25-1933-4167-8c14-2a9e2a143d0f","failed":false,"volumeDataDensity":0.00009999999999998899,"skip":false,"transient":false,"readOnly":false},"destinationVolume":{"path":"/dfs/data1/","capacity":2399304445952,"storageType":"DISK","used":1070758333399,"reserved":0,"uuid":"DS-ccc089fe-bb80-40d5-983e-fe678e7607b3","failed":false,"volumeDataDensity":0.018600000000000005,"skip":false,"transient":false,"readOnly":false},"idealStorage":0.4648,"bytesToMove":140740287938,"volumeSetID":"9bbee851-9964-4d91-8a61-41ae86901e37"},{"@class":"org.apache.hadoop.hdfs.server.diskbalancer.planner.MoveStep","sourceVolume":{"path":"/dfs/data10/","capacity":999716507648,"storageType":"DISK","used":518103326696,"reserved":0,"uuid":"DS-4ea78bac-85e4-4d7a-92f6-72d02502e30f","failed":false,"volumeDataDensity":-0.0534,"skip":false,"transient":false,"readOnly":false},"destinationVolume":{"path":"/dfs/data5/","capacity":2399304445952,"storageType":"DISK","used":1115196706478,"reserved":0,"uuid":"DS-183b713c-f95d-45f5-8f1e-530ea8a15ec1","failed":false,"volumeDataDensity":0.00009999999999998899,"skip":false,"transient":false,"readOnly":false},"idealStorage":0.4648,"bytesToMove":47840136002,"volumeSetID":"9bbee851-9964-4d91-8a61-41ae86901e37"}],"nodeName":"cdh192-22","nodeUUID":"13584e04-9fdd-468b-96da-59e6be03259b","port":9867,"timeStamp":1668651705345
}

执行计划

hdfs diskbalancer -execute  /system/diskbalancer/2022-Nov-17-10-21-45/cdh192-22.plan.json

查看计划

hdfs diskbalancer -query cdh192-22

状态说明：
PLAN_UNDER_PROGRESS 计划进行中
PLAN_DONE 计划执行完成

执行一会，查看有些许的优化了，但是这样子显然不久就又会到达90%的阈值的：

再后来百度大法，发现在还有个参数可以修改：
hdfs-site.xml
修改datanode写入策略，该配置默认是轮训，我们要改为以剩余空间考虑写入某块磁盘

dfs.datanode.fsdataset.volume.choosing.policyorg.apache.hadoop.hdfs.server.datanode.fsdataset.AvailableSpaceVolumeChoosingPolicy

以下参数是配置各个磁盘的均衡阈值的，默认为10G。
在此节点的所有数据存储的目录中，找一个占用最大的，找一个占用最小的。
如果在两者之差在10G的范围内，那么块分配的方式是轮询。如下为英文原文。

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-threshold 10737418240

通过调整以上2个参数，应该就可以达到我们期望的效果了。
即当每个目录的剩余空间的最大值和最小值差距在10G以内时，使用轮询写入，否则优先写入空间比较大的目录。