= 2009-08-27 =

 * [計畫] Hadoop 叢集維護
  * [狀況] 發現 hadoop104, hadoop106 kernel panic
 * [計畫] Hadoop 叢集維護
  * [狀況] 發現 /etc/hadoop/conf/hadoop-site.xml 中 dfs.replication 數值為 1 也就是沒做備份
  * [解法]
   1. 修改 dfs.replication 數值為 3
   2. 重新執行 hadoop-namenode 與 hadoop-datanode
   3. 使用 hadoop fs -setrep 設定目前為 1 的 /user 目錄所有檔案
{{{
root@hadoop:~# su -s /bin/sh hadoop -c "hadoop fs -setrep -R 3 /user"
}}}
   4. 使用 hadoop balancer 嘗試資料的 replication 機制是否會被執行
{{{
root@hadoop:~# su -s /bin/sh hadoop -c "hadoop balancer"
}}}
   5. 使用 hadoop fsck 嘗試資料的 replication 機制是否會被執行
{{{
root@hadoop:~# su -s /bin/sh hadoop -c "hadoop fsck / -racks"
}}}
{{{
#!sh
### 會有訊息顯示目前的 replication 數目不夠
/user/waue/input/1.txt:  Under replicated blk_-682447276956362627_16045. Target Replicas is 3 but found 1 replica(s).
### 自從誤刪 hadoop113 硬碟資料後，HDFS 狀態都是 CORRUPT，看樣子要請大家重新上傳看看了
Status: CORRUPT
 Total size:    2514937876121 B
 Total dirs:    2800
 Total files:   14972
 Total blocks (validated):      51686 (avg. block size 48658009 B)
  ********************************
  CORRUPT FILES:        1921
  MISSING BLOCKS:       4972
  MISSING SIZE:         232737717270 B
  CORRUPT BLOCKS:       4972
  ********************************
 Minimally replicated blocks:   46714 (90.38037 %)
 Over-replicated blocks:        3 (0.00580428 %)
 Under-replicated blocks:       45388 (87.81488 %)
 Mis-replicated blocks:         0 (0.0 %)
 Default replication factor:    3
 Average block replication:     1.0597067
 Corrupt blocks:                4972
 Missing replicas:              89401 (163.2239 %)
 Number of data-nodes:          17
 Number of racks:               1

The filesystem under path '/' is CORRUPT
}}}
   6. 跑過 fsck 再跑 balancer 就會看到正在嘗試做資料的 replication 副本動作
{{{
root@hadoop:~# su -s /bin/sh hadoop -c "hadoop balancer"

09/08/27 06:42:34 INFO dfs.Balancer: Need to move 12.21 GB bytes to make the cluster balanced.
09/08/27 06:42:34 INFO dfs.Balancer: Decided to move 10 GB bytes from 192.168.1.10:50010 to 192.168.1.17:50010
09/08/27 06:42:34 INFO dfs.Balancer: Decided to move 10 GB bytes from 192.168.1.1:50010 to 192.168.1.19:50010
09/08/27 06:42:34 INFO dfs.Balancer: Decided to move 10 GB bytes from 192.168.1.11:50010 to 192.168.1.16:50010
09/08/27 06:42:34 INFO dfs.Balancer: Decided to move 10 GB bytes from 192.168.1.5:50010 to 192.168.1.14:50010
09/08/27 06:42:34 INFO dfs.Balancer: Decided to move 10 GB bytes from 192.168.1.9:50010 to 192.168.1.18:50010
09/08/27 06:42:34 INFO dfs.Balancer: Will move 50 GBbytes in this iteration
2009/8/27 上午 06:42:34             0                 0 KB            12.21 GB              50 GB

09/08/27 07:29:00 INFO dfs.Balancer: Decided to move block -5073029869990347015 with a length of 64 MB bytes from 192.168.1.2:50010 to 192.168.1.15:50010 using proxy source 192.168.1.2:50010
09/08/27 07:29:00 INFO dfs.Balancer: Starting moving -5073029869990347015 from 192.168.1.2:50010 to 192.168.1.15:50010
}}}
  * [發現] Hadoop 對於 HDFS /var/lib/hadoop/cache 目錄裡的檔案還真是保護到極致了...設定了 10 個 replication 副本
{{{
-rw-r--r--  10 hadoop002 supergroup     108739 2009-08-24 22:55 /var/lib/hadoop/cache/hadoop/mapred/system/job_200908242228_0009/job.jar
}}}
 * [計畫] Hadoop 叢集維護
  * [狀況] 發現把副本設為 3 會造成空間不足，此外因為檔案數多，但都是小檔案，或許不該把 block size 設為 64Mbytes (67108864)
  * [解法] 把副本設為 2 並該把 block size 設為 4kbytes (4096)