Is there any way to setup a raid device after installation?

Question

I just set up a storage-manager server that I connect via iscsi to my main system and am trying to set up a mirrored volume. The resultant volume would be a mirror of /dev/sda1 and /dev/sdd4, however I noticed that there are no raid devices set up. (here is the output of cat /proc/mdstat)

    Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
    unused devices: <none>

Due to this I set up an LVM but this combines the 2 disks which is not what I wanted... so back to raid1... but how... mdadm?

Tried it: the output of the following command simply says "mdadm: no raid-devices specified"

    sudo mdadm --create --verbose /dev/md0 --level=raid1 /dev/sdd4 /dev/sda1

I'm assuming this is because the device /dev/md0 doesn't exist.

So my question is how/could I make /dev/md0 a raid device to work with the raid1 setup and mdadm (without reinstalling my system)? If this proves impossible, how would I set up a mirrored LVM on Ubuntu 16.04?

Any insight is appreciated. Thanks!

Answer 1

Thanks to Terrance I found this tutorial that works great

https://www.howtoforge.com/how-to-set-up-software-raid1-on-a-running-system-incl-grub2-configuration-ubuntu-10.04

basically the instructions are as follows:

    1.) Change the partition type --> fdisk /dev/sdd --> press t, select partition, l to list codes, looking for "Linux raid setup" usually fd
    2.) Do the above for every volume you plan to add --> fdisk /dev/sda | t | 1 | fd
    3.) Zero the superblock of the devices --> mdadm --zero-superblock /dev/sdd4
    4.) Create the raid device --> mdadm --create /dev/md0 --level=1 --raid-disks=2 /dev/sdd4 /dev/sda1
    5.) check to make sure device exists --> cat /proc/mdstat --> should now see your raid device
    6.) Create filesystems on our raid array --> mkfs.ntfs /dev/md0 
    7.) Mount raid array --> mount /dev/md0 /srv 
    8.) I recommend a benchmark for your array so you have an idea if something is going wrong