CyborgDroid's questions

Currently I have an Ubuntu 18.04.6 LTS server with 2 6TB HDs setup in RAID1 like so:

~$ cat /proc/mdstat
Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sdd2[0] sdb2[1]
      5859412992 blocks super 1.2 [2/2] [UU]
      bitmap: 1/44 pages [4KB], 65536KB chunk

The space on the drives will run out soon so I bought 2 16TB HDs I want to add (already physically connected in the server but not setup). From what I understand I cannot add these as a separate raid1 configuration (16TB mirroring + 6TB mirroring) and need to move to raid 10. Is this true? I can't just have the two 16TB also in RAID1 and mounted as a different folder?

Can I use the 2x 16TB HDs in combination with the 2x 6TB ones in a RAID 10 or do they all have to be the same size?

How do I go about adding the 2 HDs and migrating to the new RAID setup without losing the existing data?

Business requirements:

1. Redundancy / Fault tolerance
2. Fast read/write (big data)
3. Increase HD space, does not necessarily have to act as one drive (can be a new mount point / folder if easier)

UPDATE:

Following the instructions at the link below, I added the two drives as an additional raid1 using the following commands, rebooted the computer, and now can't ssh into it.

https://www.digitalocean.com/community/tutorials/how-to-create-raid-arrays-with-mdadm-on-ubuntu-18-04#creating-a-raid-1-array

~$ lsblk -o NAME,SIZE,FSTYPE,TYPE,MOUNTPOINT
NAME            SIZE FSTYPE            TYPE  MOUNTPOINT
sda            14.6T                   disk
sdb             5.5T                   disk
├─sdb1          953M vfat              part
└─sdb2          5.5T linux_raid_member part
  └─md0         5.5T LVM2_member       raid1
    ├─vg-swap 186.3G swap              lvm   [SWAP]
    ├─vg-root  93.1G ext4              lvm   /
    ├─vg-tmp   46.6G ext4              lvm   /tmp
    ├─vg-var   23.3G ext4              lvm   /var
    └─vg-home   5.1T ext4              lvm   /home
sdc            14.6T                   disk
sdd             5.5T                   disk
├─sdd1          953M vfat              part  /boot/efi
└─sdd2          5.5T linux_raid_member part
  └─md0         5.5T LVM2_member       raid1
    ├─vg-swap 186.3G swap              lvm   [SWAP]
    ├─vg-root  93.1G ext4              lvm   /
    ├─vg-tmp   46.6G ext4              lvm   /tmp
    ├─vg-var   23.3G ext4              lvm   /var
    └─vg-home   5.1T ext4              lvm   /home

~$ sudo mdadm --create --verbose /dev/md1 --level=1 --raid-devices=2 /dev/sda /dev/sdc
sudo mkfs.ext4 -F /dev/md1
sudo mkdir -p /mnt/md1
sudo mount /dev/md1 /mnt/md1

~$ df -h -x devtmpfs -x tmpfs
Filesystem           Size  Used Avail Use% Mounted on
/dev/mapper/vg-root   92G  7.5G   79G   9% /
/dev/sdd1            952M  4.4M  947M   1% /boot/efi
/dev/mapper/vg-var    23G  6.0G   16G  28% /var
/dev/mapper/vg-tmp    46G   54M   44G   1% /tmp
/dev/mapper/vg-home  5.1T  2.5T  2.4T  51% /home
/dev/md1              15T   19M   14T   1% /mnt/md1

~$ sudo mdadm --detail --scan | sudo tee -a /etc/mdadm/mdadm.conf
ARRAY /dev/md/0 metadata=1.2 name=mypc:0 UUID=someweirdhash
ARRAY /dev/md1 metadata=1.2 name=mypc:1 UUID=someweirdhash

~$ sudo update-initramfs -u
update-initramfs: Generating /boot/initrd.img-4.15.0-166-generic

~$ sudo reboot

Cannot ssh into server after reboot.

DID NOT DO THIS: (what are the last two zeros below?) I wasn't sure what this command does and imagined it could set the new array to be the boot one, so maybe not running it broke it:

~$ echo '/dev/md1 /mnt/md1 ext4 defaults,nofail,discard 0 0' | sudo tee -a /etc/fstab

I installed Ubuntu Server 18.04 with the LVM option and left the default partition setup. Now my main drive only has 4GB in a 1TB hard drive. How can I fix this without starting from scratch?

Results of df -h :

Filesystem                         Size    Used Available Use% Mounted on
udev                                16G       0       16G   0% /dev
tmpfs                               32G    1.7M       32G   1% /run
/dev/mapper/ubuntu--vg-ubuntu--lv  3.9G    3.6G       92M  98% /    
tmpfs                               16G       0       16G   0% /dev/shm
tmpfs                              5.0M       0      5.0M   0% /run/lock
tmpfs                               16G       0       16G   0% /sys/fs/cgroup
/dev/loop0                          87M     87M         0 100% /snap/core/4917
/dev/loop1                         3.2M    3.2M         0 100% /snap/stress-ng/471
/dev/loop2                          90M     90M         0 100% /snap/core/6130
/dev/sda2                          976M    143M      766M  16% /boot
tmpfs                              3.2G       0      3.2G   0% /run/user/1000