Resize the /dev/root partition

Question

I have a dedicated server in ovh on which I have

/dev/md3 1.8T /home 1,7T

and I have a partition that has only 20GB

/dev/root 20G 19G 3,7G 99% /

And the database stops working all the time because there is no place. Now I would like to reduce the partition home or / dev / md3 by eg 100GB, and add 100GB to the / dev / root partition as I can do it without corrupting the whole system? :( Of course, there is a centos system with DirectAdmin installed, no graphical environment, so only consoles are left.

This size was set by DA during the automatic installation by the OVH panel, and currently there are 120 domains with Wordpress on the server.

df result

Filesystem      1K-blocks     Used  Available Use% Mounted on
/dev/root        20026172 15027060    3958784  80% /
devtmpfs         16415192        0   16415192   0% /dev
tmpfs            16450184       28   16450156   1% /dev/shm
tmpfs            16450184  1681448   14768736  11% /run
tmpfs            16450184        0   16450184   0% /sys/fs/cgroup
/dev/md3       1902052420 13841064 1791569672   1% /home
tmpfs             3290040        0    3290040   0% /run/user/0

lsblk result

NAME    MAJ:MIN RM    SIZE RO TYPE  MOUNTPOINT
sdb       8:16   0    1.8T  0 disk
├─sdb4    8:20   0    511M  0 part  [SWAP]
├─sdb2    8:18   0   19.5G  0 part
│ └─md2   9:2    0   19.5G  0 raid1 /
├─sdb3    8:19   0    1.8T  0 part
│ └─md3   9:3    0    1.8T  0 raid1 /home
└─sdb1    8:17   0 1004.5K  0 part
sda       8:0    0    1.8T  0 disk
├─sda4    8:4    0    511M  0 part  [SWAP]
├─sda2    8:2    0   19.5G  0 part
│ └─md2   9:2    0   19.5G  0 raid1 /
├─sda3    8:3    0    1.4T  0 part
│ └─md3   9:3    0    1.8T  0 raid1 /home
└─sda1    8:1    0 1004.5K  0 part

Answer 1

If moving the database directory to /home is an option, you may follow these steps

• Stop the mysql server
• Copy the directory from /var/lib/mysql to /home/mysql

• Change or add a line

  [mysqld]
  datadir = /home/mysql
  

• Start the mysql server

Answer 2

Given the tiny amount of data that is stored on the system (less than 30 GB) and the amount of effort you would need to

• shrink the filesystem on md3
• shrink md3 itself
• shrink sda3 and sdb3
• move sda3 and sdb3 to the end of the drive
• grow sda2 and sdb2
• grow md2
• grow the filesystem on md2

I would strongly suggest you just take a backup, reinstall the system with different partitioning and restore from your backup.

You can save a lot of headache, effort and downtime this way.

I strongly suggest you set up the new partitioning scheme using LVM and assign only as much space to each filesystem as is required. Later on-line growing is really easy while on-line shrinking is usually impossible.