Changes

You can refer to 'man mdadm' or http://www.linuxmanpages.com/man8/mdadm.8.php

You can refer to 'man mdadm' or http://www.linuxmanpages.com/man8/mdadm.8.php

Sometimes a partition will be taken offline automatically. This will happen if, for example, a read or write error is detected in a disk in the RAID set, or a disk does not respond fast enough, causing a timeout. When this happens, the details of the raid can be seen by inspecting the mdstat file. In the following example, partition hda2 (hard disk 'a', partition 2) is offline:

Sometimes a partition will be taken offline automatically. Admin will receive an email '''DegradedArray event on /dev/md2'''.

 

This will happen if, for example, a read or write error is detected in a disk in the RAID set, or a disk does not respond fast enough, causing a timeout. When this happens, the details of the raid can be seen by inspecting the mdstat file.

  [root@sme]# cat /proc/mdstat

  [root@sme]# cat /proc/mdstat

       38837056 blocks [2/2] [UU]

       38837056 blocks [2/2] [UU]

   

   

  md2 : active raid1 hdb2[1]

  md2 : active raid1 hdb2[1]       <-- missing partition 

       1048704 blocks [2/1] [_U]

       1048704 blocks [2/1] [_U]   <-- failed

   

   

  md0 : active raid1 hda1[0] hdb1[1]

  md0 : active raid1 hda1[0] hdb1[1]

       255936 blocks [2/2] [UU]

       255936 blocks [2/2] [UU]

Make a note of the raid partition that has failed, shown by '''[_U]''' <br>

[root@sme ~]# mdadm --detail /dev/md2

In this case it is md2, the device being /dev/md2.

To recover this raid, i.e. to get it back into sync, you need to use the 'mdadm --add' command.

Determine the missing physical partition, Look carefully, and fill in the gap, <br>

 

in this example, it's hda2, the device being /dev/hda2

Make a note of the raid partition that has failed. In this case it is md2, the device being /dev/md2/. You will need to add the physical partition back into that raid partition. The missing physical partition in the above example is /dev/hda2

md2 : active raid1 '''hda2[0]''' hdb2[1]

The command to run to re-add is then:

To add the physical partition back into that raid partition.

  [root@sme]# mdadm --add /dev/md2 /dev/hda2

  [root@sme]# mdadm --add /dev/md2 /dev/hda2