Extend LVM when all 4 primary partitions have been taken

Solution 1:

Took the afternoon to study up on LVM and found a solution. So, my initial solution turns out to be a working solution. Here's what I did.

1. Use fdisk to make /dev/vda4 bigger. To do that delete partition 4, re-add it as a primary partition and let it make use of all available sectors. It'll ask you about deleting the LVM2_member signature, make sure to answer no. Set partition type to Linux LVM (8e). Write the new partition table.
2. pvresize /dev/vda4.
3. lvextend -l +100%FREE /dev/vg_directadmin/lv_root.
4. Finally you need to resize /dev/vg_directadmin/lv_root with resize2fs (or xfs_growfs on CentOS 7 if I'm not mistaken). I had to do a disk check as well with e2fsck -f /dev/vg_directadmin/lv_root followed by resize2fs /dev/vg_directadmin/lv_root.
5. Finally, remount.

Hope this helps someone else. Linux LVM on HowToForge is a helpful tutorial as well!