HDFS banlancer重平衡

1、優化參數

1.設置線程數

        指定用於在DataNode間傳輸block數據的最大線程數

        dfs.datanode.max.transfer.threads = 4096

        （裝有HBASE時可適當提高此值，老版本爲dfs.datanode.max.xcievers）

2.設置平衡帶寬

        指定DataNode用於balancer的帶寬，默認是1048576(1MB)單位爲Byte，一般可設置爲10MB；若機器性能優異能夠設定爲30-50MB；若是機器的網卡和交換機的帶寬有限，能夠設爲1-10MB

        dfs.datanode.balance.bandwidthPerSec  = 31457280

3.設置balance線程數

        指定DataNode上同時用於balance待移動block的最大線程個數，這個值默認是5

        dfs.datanode.balance.max.concurrent.moves = 50

2、運行balancer

1.balancer理論步驟

        1) 從namenode獲取datanode磁盤的使用狀況
        2) 計算須要把哪些數據移動到哪些節點
        3) 分別移動，完成後刪除舊的block信息
        4) 循環執行，直到達到平衡標準

2.執行balancer

#臨時設置帶寬（10MB）
sudo -u hdfs hdfs dfsadmin -setBalancerBandwidth 10240000 

#各節點存儲的浮動比例10%上下浮動
sudo -u hdfs hdfs balancer -threshold 10

3.監控日誌

        1）出現報錯日誌

org.apache.hadoop.ipc.RemoteException(org.apache.hadoop.ipc.StandbyException): Operation category READ is not supported in state standby.

        此報錯信息一般出如今配置了HA的HDFS中，balancer執行時不知道哪一個namenode爲active哪一個爲standby，當鏈接到standby的namenode時會出現如下報錯。無須擔憂只要集羣中爲一個active狀態的namenode，進程會嘗試鏈接active狀態的namenode，程序可以正常執行。

        2）程序繼續正常執行

INFO - Jul 28, 2017 3:32:04 PM          32             23.39 GB            22.80 GB              30 GB
17/07/28 15:32:13 INFO net.NetworkTopology: Adding a new node: /rack1/192.168.111.27:50010
17/07/28 15:32:13 INFO net.NetworkTopology: Adding a new node: /rack1/192.168.111.22:50010
17/07/28 15:32:13 INFO net.NetworkTopology: Adding a new node: /rack1/192.168.111.23:50010
17/07/28 15:32:13 INFO net.NetworkTopology: Adding a new node: /rack1/192.168.111.25:50010
17/07/28 15:32:13 INFO net.NetworkTopology: Adding a new node: /rack2/192.168.111.34:50010
17/07/28 15:32:13 INFO net.NetworkTopology: Adding a new node: /rack1/192.168.111.29:50010
17/07/28 15:32:13 INFO net.NetworkTopology: Adding a new node: /rack2/192.168.111.39:50010
17/07/28 15:32:13 INFO net.NetworkTopology: Adding a new node: /rack2/192.168.111.32:50010
17/07/28 15:32:13 INFO net.NetworkTopology: Adding a new node: /rack2/192.168.111.33:50010
17/07/28 15:32:13 INFO net.NetworkTopology: Adding a new node: /rack1/192.168.111.28:50010
17/07/28 15:32:13 INFO net.NetworkTopology: Adding a new node: /rack1/192.168.111.26:50010
17/07/28 15:32:13 INFO net.NetworkTopology: Adding a new node: /rack2/192.168.111.37:50010
17/07/28 15:32:13 INFO net.NetworkTopology: Adding a new node: /rack1/192.168.111.24:50010
17/07/28 15:32:13 INFO net.NetworkTopology: Adding a new node: /rack2/192.168.111.35:50010
17/07/28 15:32:13 INFO net.NetworkTopology: Adding a new node: /rack2/192.168.111.38:50010
17/07/28 15:32:13 INFO net.NetworkTopology: Adding a new node: /rack2/192.168.111.36:50010
17/07/28 15:32:13 INFO balancer.Balancer: 1 over-utilized: [192.168.111.37:50010:DISK]
17/07/28 15:32:13 INFO balancer.Balancer: 3 underutilized: [192.168.111.25:50010:DISK, 192.168.111.35:50010:DISK, 192.168.111.36:50010:DISK]
17/07/28 15:32:13 INFO balancer.Balancer: Need to move 22.58 GB to make the cluster balanced.
17/07/28 15:32:13 INFO balancer.Balancer: Decided to move 10 GB bytes from 192.168.111.37:50010:DISK to 192.168.111.35:50010:DISK
17/07/28 15:32:13 INFO balancer.Balancer: Decided to move 10 GB bytes from 192.168.111.27:50010:DISK to 192.168.111.25:50010:DISK
17/07/28 15:32:13 INFO balancer.Balancer: Decided to move 7.83 GB bytes from 192.168.111.39:50010:DISK to 192.168.111.36:50010:DISK
17/07/28 15:32:13 INFO balancer.Balancer: Decided to move 2.17 GB bytes from 192.168.111.32:50010:DISK to 192.168.111.36:50010:DISK
17/07/28 15:32:13 INFO balancer.Balancer: Will move 30 GB in this iteration
17/07/28 15:32:13 INFO balancer.Dispatcher: Successfully moved blk_1079961644_6305194 with size=41 from 192.168.111.39:50010:DISK to 192.168.111.36:50010:DISK through 192.168.111.39:50010
17/07/28 15:32:13 INFO balancer.Dispatcher: Successfully moved blk_1079963221_6306771 with size=41 from 192.168.111.39:50010:DISK to 192.168.111.36:50010:DISK through 192.168.111.39:50010
17/07/28 15:32:13 INFO balancer.Dispatcher: Successfully moved blk_1075009112_1268291 with size=99980 from 192.168.111.27:50010:DISK to 192.168.111.25:50010:DISK through 192.168.111.27:50010
17/07/28 15:32:13 INFO balancer.Dispatcher: Successfully moved blk_1079960720_6304270 with size=5234467 from 192.168.111.39:50010:DISK to 192.168.111.36:50010:DISK through 192.168.111.39:50010