MariaDB no space for database!

Hi,
Wordpress login kept redirecting to reauth=1 so I enabled debug and found this:
WordPress database error: [Can't change size of file (Errcode: 28 "No space left on device")]
SHOW FULL COLUMNS FROM `11631_options`

And

---

WordPress database error: [Can't change size of file (Errcode: 28 "No space left on device")]
SELECT t.*, tt.*, tr.object_id FROM 11631_terms AS t INNER JOIN 11631_term_taxonomy AS tt ON tt.term_id = t.term_id INNER JOIN 11631_term_relationships AS tr ON tr.term_taxonomy_id = tt.term_taxonomy_id WHERE tt.taxonomy IN ('category', 'post_tag', 'post_format') AND tr.object_id IN (30504, 30506, 30508, 30514, 30516, 30518, 30520, 30527, 30532, 30553) ORDER BY t.name ASC

 

Also the VPS has enough space:
http://puu.sh/stMNi/f028ea5cfd.png

 

Yum, you are right. is there any way for this:
http://puu.sh/stNH2/c9bb3de75a.png

The vps got 80 GB space, but only 26 GB in home!

 

4.0K /home/mysqltmp
20G /home/nginx
16K /home/lost+found
8.0K /home/.ccache
24G /home

 

from 80 GB only 26 GB goes to home. What is the "root" for then? Is it for nginx? I can reinstall the VPS, but what partition do you recommend?

[root@localhost ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root
50G 6.7G 40G 15% /
tmpfs 1.9G 0 1.9G 0% /dev/shm
/dev/sda1 477M 52M 400M 12% /boot
/dev/mapper/VolGroup-lv_home
26G 24G 36M 100% /home
/home/usertmp_donotdelete
3.9G 13M 3.6G 1% /tmp

 

Thank you for the help, I extended the home partition, but still wonder why is it wasting the whole 50 GB!