Remove software RAID device using mdadm

Removing one mdraid device/partition is quite easy. This process should not require reboot (but it is still recommended). Note: this process will make your data unreadable.

Step 1: Identify the RAID device

First, you need to identify the RAID device that you want to remove. You can list all RAID devices using the following command:

cat /proc/mdstat

Note down which RAID device (mdX) you want to remove. Also note its disk partitions (you can also list them using the lsblk command).

Step 2: Unmount the RAID partition (if mounted) and edit /etf/fstab

If the to-be-removed-device contains any partition currently mounted to your system, unmount it.

sudo umount /some/partition

Now remove the partition from /etc/fstab so it the system won’t try to mount it after the next reboot.

Step 3: Stop the RAID Device and remove it from /etc/mdadm/mdadm.conf

Now stop the RAID device using the mdadm tool.

sudo mdadm --stop /dev/mdX

Now edit the mdadm config file (/etc/mdadm/mdadm.conf) and remove the device from there.

Step 4: Remove the RAID Device

You can remove the RAID device

sudo mdadm --remove /dev/mdX

Note: if this won’t command gives an error about non-existing device, reboot the system and remove the raid afterwards.

Step 5: Remove RAID superblocks

Now you should zero the superblocks on the individual disks that were part of the RAID. This can prevent them from being automatically reassembled into a RAID array in the future. Remember — you do this on the disk partitions (/dev/sdX) and NOT on the RAID device (/dev/mdX).

sudo mdadm --zero-superblock /dev/sdX1 /dev/sdX2

Optional: overwrite disks with random data

If you want to try to remove the data from disk, you can rewrite it using dd.

dd if=/dev/urandom bs=4096 of=/dev/sdX

Note1: you can use /dev/random on the systems like Debian 11+ and Ubuntu 22.04+, since it is non-blocking there.

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Note2: this is not a secure way of erasing data, especially on NVMe drives.

This story was originally published on DevOps Advocate — How to remove mdraid.