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Managing an MD Device
Removing and Adding an MD Mirror Component Disk
Appendix A 101
Removing and Adding an MD Mirror
Component Disk
There are certain failure scenarios, where you would need to manually
remove the mirror component of an MD device and add it again later. For
example, if links between two data centers fail, you would need to
remove and add the disks that were marked as failed disks.
When a disk within an MD device fails, the /proc/mdstat file of the MD
array displays a message. For example:
[root@dlhct1 dev]# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sde[2](F) sdf[0]
9766784 blocks [2/1] [U_]
unused devices: <none>
In the message, the (F) indicates which disk has failed. In this example,
the sde[2] disk has failed.
In such a scenario, you must remove the failed disk from the MD array.
You need to determine the persistent name of the failed disk before you
remove it from the MD array. For this example, run the following
command to determine the persistent name of the disk:
# udevinfo -q symlink -n sdc1
Following is a sample output:
hpdev/mylink-sdc \
disk/by-id/scsi-3600805f3000b9510a6d7f8a6cdb70054-part1 \
disk/by -path/pci-0000:06:01.0-scsi-0:0:1:30-part1
Run the following command to remove a failed component device from
the MD array:
# mdadm - -remove <md device name>
<md_mirror_component_persistent_name>
In this example:
# mdadm --remove /dev/md0 /dev/hpdev/mylink-sdc1
This command removes the failed mirrored disk from the array.