Your root partition is way too big. The remaining18 GB will never be used
Code:
Size Used Avail Capacity Mounted on
19G 197M 18G 1% /
Actually 500 MB is more than enough for this partition.
For a server it is also recommended to have a separate partitions for
//var/log and
/var/tmp.
If you offer mail facilities to your users you also need a separate
/var/mail.
And you are ignoring my advice to separate the base system, application and user generated data.
