今天一台服务器 datanode服务自动停止了，查看datanode log发现如下报错：
org.apache.hadoop.util.DiskChecker$DiskErrorException: Too many failed volumes - current valid volumes: 1, volumes configured: 2, volumes failed: 1, volume failures tolerated: 0
意思是volumes出现故障，在hdfs-site.xml文件中有个配置:
<property>
<name>dfs.datanode.data.dir</name>
<value>/diskb/hadoop/hdfs/data,/diskc/hadoop/hdfs/data,/diskd/hadoop/hdfs/data</value>
</property>
<property>
<name>
dfs.datanode.failed.volumes.tolerated</name>
<value>0</value>
</property>
dfs.datanode.failed.volumes.tolerated值为0，意思是当diska、diskb、diskc、diskd任何一块磁盘出现问题后，
datanode就会服务停止，如何设置为1，可以有一块故障。
#dmesg
出现大量I/O错误：
sd 3:0:0:0: [sdd] Unhandled error code
sd 3:0:0:0: [sdd] Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
sd 3:0:0:0: [sdd] CDB: Read(16): 88 00 00 00 00 01 51 00 01 2a 00 00 00 30 00 00
__ratelimit: 8 callbacks suppressed
sd 3:0:0:0: [sdd] Unhandled error code
sd 3:0:0:0: [sdd] Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
sd 3:0:0:0: [sdd] CDB: Read(16): 88 00 00 00 00 01 51 00 01 32 00 00 00 28 00 00
EXT4-fs error (device sdd1): __ext4_get_inode_loc: unable to read inode block - inode=2760773, block=706740260
sd 3:0:0:0: [sdd] Unhandled error code
sd 3:0:0:0: [sdd] Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
sd 3:0:0:0: [sdd] CDB: Read(16): 88 00 00 00 00 01 51 00 01 2a 00 00 00 30 00 00
sd 3:0:0:0: [sdd] Unhandled error code
sd 3:0:0:0: [sdd] Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
sd 3:0:0:0: [sdd] CDB: Read(16): 88 00 00 00 00 01 51 00 01 32 00 00 00 28 00 00
EXT4-fs error (device sdd1): __ext4_get_inode_loc: unable to read inode block - inode=2760802, block=706740262
sd 3:0:0:0: [sdd] Unhandled error code
sd 3:0:0:0: [sdd] Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
sd 3:0:0:0: [sdd] CDB: Read(16): 88 00 00 00 00 01 51 00 01 2a 00 00 00 30 00 00
EXT4-fs error (device sdd1): __ext4_get_inode_loc: unable to read inode block - inode=2760734, block=706740257
sd 3:0:0:0: [sdd] Unhandled error code
sd 3:0:0:0: [sdd] Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
sd 3:0:0:0: [sdd] CDB: Read(10): 28 00 11 80 01 2a 00 00 08 00
sd 3:0:0:0: [sdd] Unhandled error code
sd 3:0:0:0: [sdd] Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
sd 3:0:0:0: [sdd] CDB: Read(10): 28 00 11 80 01 3a 00 00 10 00
sd 3:0:0:0: [sdd] Unhandled error code
sd 3:0:0:0: [sdd] Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
sd 3:0:0:0: [sdd] CDB: Read(10): 28 00 11 80 01 52 00 00 08 00
sd 3:0:0:0: [sdd] Unhandled error code
sd 3:0:0:0: [sdd] Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
sd 3:0:0:0: [sdd] CDB: Read(10): 28 00 11 80 01 62 00 00 08 00
sd 3:0:0:0: [sdd] Unhandled error code
sd 3:0:0:0: [sdd] Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
sd 3:0:0:0: [sdd] CDB: Read(10): 28 00 11 80 01 42 00 00 08 00
end_request: I/O error, dev sdd, sector 293601570
EXT4-fs error (device sdd1): __ext4_get_inode_loc: unable to read inode block - inode=143361, block=36700192
end_request: I/O error, dev sdd, sector 5750391074
EXT4-fs error (device sdd1): __ext4_get_inode_loc: unable to read inode block - inode=2807809, block=718798880
end_request: I/O error, dev sdd, sector 5653922090
尝试新建文件报错如下：
#touch 111
touch: cannot touch `111': Read-only file system
硬盘的健康状况：
smartctl -H /dev/sdd
注意
result后边的结果：PASSED，这表示硬盘健康状态良好
如果这里显示Failure，那么最好立刻给服务器更换硬盘
可以肯定是这块sdd硬盘出现问题，可以将此节点服务器，从hadoop群集中排除，
umount这块硬盘，之后更换个新的，重新格式化mount，再将服务器重新加入到hadoop群集中即可。
网上有些朋友说进行linux修复模式，fsck下硬盘，但是为了避免再出现问题，还是直接换个新的。
