Friday, 27 September 2013

Fixing a broken mdadm array – failed drive

Sometimes, even with the best intentions things can go wrong with a RAID array. A drive may fail, or the array may become ‘dirty’ for any number of reasons.

Here, we will go through some simple steps to repair a damaged array.

In our example case, a drive has failed. By running the following command in a terminal, we can get a status update on our array:

    sudo mdadm --detail /dev/md0 # Displays detail about /dev/md0

The output:

failed.png

You can see the state is listed as “clean, degraded” this means a drive is missing from the array. Also note that device 1 has been “removed”.

Before we do anything, we need to unmount our array (in this case, /dev/md0)

    sudo umount /dev/md0 # Unmounts /dev/md0

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