hadoop集群运行过程中，节点的块状态或者上下线节点时集群都会受影响。
如何查看当前的hdfs的块的状态
hadoop1.x时候的命令，hadoop2.x也可使用：
hadoop fsck /
在hadoop2.0之后，可以使用新命令：
hdfs fsck /
[root@node01 ~]# su hdfs -c "hadoop fsck /"
WARNING: Use of this script to execute fsck is deprecated.
WARNING: Attempting to execute replacement "hdfs fsck" instead.
Connecting to namenode via http://node01:9870/fsck?ugi=hdfs&path=%2F
FSCK started by hdfs (auth:SIMPLE) from /192.168.1.81 for path / at Wed Apr 29 09:19:27 CST 2020
Status: HEALTHY
Number of data-nodes: 3
Number of racks: 1
Total dirs: 1884
Total symlinks: 0
Replicated Blocks:
Total size: 387368629 B
Total files: 85
Total blocks (validated): 85 (avg. block size 4557277 B)
Minimally replicated blocks: 85 (100.0 %)
Over-replicated blocks: 0 (0.0 %)
Under-replicated blocks: 0 (0.0 %)
Mis-replicated blocks: 0 (0.0 %)
Default replication factor: 3
Average block replication: 3.0
Missing blocks: 0
Corrupt blocks: 0
Missing replicas: 0 (0.0 %)
Blocks queued for replication: 0
Erasure Coded Block Groups:
Total size: 0 B
Total files: 0
Total block groups (validated): 0
Minimally erasure-coded block groups: 0
Over-erasure-coded block groups: 0
Under-erasure-coded block groups: 0
Unsatisfactory placement block groups: 0
Average block group size: 0.0
Missing block groups: 0
Corrupt block groups: 0
Missing internal blocks: 0
Blocks queued for replication: 0
FSCK ended at Wed Apr 29 09:19:28 CST 2020 in 542 milliseconds
The filesystem under path '/' is HEALTHY
参数说明：
-
Total size ： hdfs集群存储大小，不包括复本大小。如：75423236058649 B （字节）。（字节->KB->m->G->TB，75423236058649/1024/1024/1024/1024=68.59703358591014TB）
-
Total blocks (validated) : 总共的块数量，不包括复本。（5363690 (avg. block size 14061818 B) (Total open file blocks (not validated): 148)，计算： 14061818 *5363690=75423232588420 集群的容量大小，不包括复本的）
-
Number of data-nodes ： datanode的节点数量
-
Number of racks ： 机架数量
-
Default replication factor ： 默认的复制因子
-
Average block replication ： 当前块的平均复制数，如果小 default replication factor，则有块丢失
-
Under-replicated blocks ： 正在复制块数量，可采用 hadoop fsck -blocks 解决问题
-
Mis-replicated blocks ： 正复制的缺少复制块的数量
-
Missing replicas ： 缺少复制块的数量，通常情况下Under-replicated blocks\Mis-- replicated blocks\Missing replicas 都为0，则集群健康，如果不为0，则缺失块了
-
Corrupt blocks ： 坏块的数量，这个值不为0，则说明当前集群有不可恢复的块，即数据有丢失了
当下架节点时Under-replicated blocks\Mis-replicated blocks\Missing replicas，这三个参数会显示当前，需要补的块的数量，集群会自动补全，当三个参数都为0时，则集群块的复制块完全了。
[root@node01 ~]# su hdfs -c "hdfs fsck -list-corruptfileblocks"
Connecting to namenode via http://node01:9870/fsck?ugi=hdfs&listcorruptfileblocks=1&path=%2F
The filesystem under path '/' has 0 CORRUPT files
[root@node01 ~]# su hdfs -c "hdfs fsck / | egrep -v '^\.+$' | grep -v eplica"
Connecting to namenode via http://node01:9870/fsck?ugi=hdfs&path=%2F
FSCK started by hdfs (auth:SIMPLE) from /192.168.1.81 for path / at Wed Apr 29 09:27:20 CST 2020
Status: HEALTHY
Number of data-nodes: 3
Number of racks: 1
Total dirs: 1890
Total symlinks: 0
Total size: 387368629 B
Total files: 85
Total blocks (validated): 85 (avg. block size 4557277 B)
Missing blocks: 0
Corrupt blocks: 0
Erasure Coded Block Groups:
Total size: 0 B
Total files: 0
Total block groups (validated): 0
Minimally erasure-coded block groups: 0
Over-erasure-coded block groups: 0
Under-erasure-coded block groups: 0
Unsatisfactory placement block groups: 0
Average block group size: 0.0
Missing block groups: 0
Corrupt block groups: 0
Missing internal blocks: 0
FSCK ended at Wed Apr 29 09:27:20 CST 2020 in 96 milliseconds
The filesystem under path '/' is HEALTHY
