How to merge RAID1 partitions in Ubuntu?

Question

ubuntu

There is a server with 2x480Gb SSD in RAID1
And this is the picture

Filesystem      Size  Used Avail Use% Mounted on
udev             16G     0   16G   0% /dev
tmpfs           3.2G   14M  3.2G   1% /run
/dev/md2         20G  2.3G   16G  13% /
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/md1        487M   28M  430M   7% /boot
/dev/md3        420G   71M  399G   1% /home

How to merge /dev/md3 with /dev/md2 i.e. increase the size of /dev/md2 and delete /dev/md3?
The data in /home is not important.

Answer 1

Suppose given - disks sda and sdb, sda1 and sdb1 in md1, sda2 and sdb2 in md2, sda3 and sdb3 in md3
The procedure looks like this -
1. umount /home && mkdir /mnt/home && mount /dev/md3 /mnt/ home
2. cp -rp /mnt/home/* /home
3. remove the md3 array
4. mark one disk in the md2 array as bad and remove it from the link array (assume sdb2)
5. edit fstab to mount the system root with sdb2
6 . delete the partition that participated in md3 - sdb3 and resize the sdb2 partition to the desired size
7. reboot
8. delete the md2 array, link above
9. delete the sda3 partition and move the sda2 partition to exactly match the sdb2 partition
10. Re-create the md2 array and edit fstab to mount the root with md2
11. Profit
But first I would "practice on cats"

Answer 2

lvm