上传:
-bash-4.2$ hdfs dfs -mkdir /blockrecover
-bash-4.2$ echo "www.ruozedata.com" > ruozedata.md

-bash-4.2$ hdfs dfs -put ruozedata.md /blockrecover
-bash-4.2$ hdfs dfs -ls /blockrecover
Found 1 items
-rw-r--r--   3 hdfs supergroup         18 2019-03-03 14:42 /blockrecover/ruozedata.md
-bash-4.2$ 

校验: 健康状态
-bash-4.2$ hdfs fsck /
Connecting to namenode via http://yws76:50070/fsck?ugi=hdfs&path=%2F
FSCK started by hdfs (auth:SIMPLE) from /192.168.0.76 for path / at Sun Mar 03 14:44:44 CST 2019
...............................................................................Status: HEALTHY
 Total size:    50194618424 B
 Total dirs:    354
 Total files:   1079
 Total symlinks:                0
 Total blocks (validated):      992 (avg. block size 50599413 B)
 Minimally replicated blocks:   992 (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
 Corrupt blocks:                0
 Missing replicas:              0 (0.0 %)
 Number of data-nodes:          3
 Number of racks:               1
FSCK ended at Sun Mar 03 14:44:45 CST 2019 in 76 milliseconds

The filesystem under path '/' is HEALTHY
-bash-4.2$

删除块和meta文件:
[root@yws87 subdir135]# rm -rf blk_1075808214 blk_1075808214_2068515.meta

直接重启HDFS，直接模拟损坏效果，然后fsck检查:
-bash-4.2$ hdfs fsck /
Connecting to namenode via http://yws77:50070/fsck?ugi=hdfs&path=%2F
FSCK started by hdfs (auth:SIMPLE) from /192.168.0.76 for path / at Sun Mar 03 16:02:04 CST 2019
.
/blockrecover/ruozedata.md:  Under replicated BP-1513979236-192.168.0.76-1514982530341:blk_1075808214_2068515. Target Replicas is 3 but found 2 live replica(s), 0 decommissioned replica(s), 0 decommissioning replica(s).
...............................................................................Status: HEALTHY
 Total size:    50194618424 B
 Total dirs:    354
 Total files:   1079
 Total symlinks:                0
 Total blocks (validated):      992 (avg. block size 50599413 B)
 Minimally replicated blocks:   992 (100.0 %)
 Over-replicated blocks:        0 (0.0 %)
 Under-replicated blocks:       1 (0.10080645 %)
 Mis-replicated blocks:         0 (0.0 %)
 Default replication factor:    3
 Average block replication:     2.998992
 Corrupt blocks:                0
 Missing replicas:              1 (0.033602152 %)
 Number of data-nodes:          3
 Number of racks:               1
FSCK ended at Sun Mar 03 16:02:04 CST 2019 in 148 milliseconds


The filesystem under path '/' is HEALTHY
-bash-4.2$

-bash-4.2$ hdfs |grep debug
没有输出debug参数的任何信息结果！
故hdfs命令帮助是没有debug的，但是确实有hdfs debug这个组合命令，切记。

修复命令:
-bash-4.2$ hdfs debug  recoverLease  -path /blockrecover/ruozedata.md -retries 10
recoverLease SUCCEEDED on /blockrecover/ruozedata.md
-bash-4.2$ 

直接DN节点查看，block文件和meta文件恢复:
[root@yws87 subdir135]# ll
total 8
-rw-r--r-- 1 hdfs hdfs 56 Mar  3 14:28 blk_1075808202
-rw-r--r-- 1 hdfs hdfs 11 Mar  3 14:28 blk_1075808202_2068503.meta
[root@yws87 subdir135]# ll
total 24
-rw-r--r-- 1 hdfs hdfs 56 Mar  3 14:28 blk_1075808202
-rw-r--r-- 1 hdfs hdfs 11 Mar  3 14:28 blk_1075808202_2068503.meta
-rw-r--r-- 1 hdfs hdfs 18 Mar  3 15:23 blk_1075808214
-rw-r--r-- 1 hdfs hdfs 11 Mar  3 15:23 blk_1075808214_2068515.meta

当数据块损坏后，DN节点执行directoryscan操作之前，都不会发现损坏；
也就是directoryscan操作是间隔6h
dfs.datanode.directoryscan.interval : 21600

在DN向NN进行blockreport前，都不会恢复数据块;
也就是blockreport操作是间隔6h
dfs.blockreport.intervalMsec : 21600000

当NN收到blockreport才会进行恢复操作。