I have a older server I am working on that was setup by someone else which is reporting "Insufficient system storage" when trying to send mail.

Here is the output from df -h

Filesystem Size Used Avail Use% Mounted on
/dev/md3 4.9G 615M 4.3G 13% /
/dev/md5 997M 45M 952M 5% /boot
/dev/md1 7.9G 6.6G 1.3G 84% /home
/dev/md4 1.7G 33M 1.7G 2% /tmp
/dev/md0 9.8G 1.7G 8.2G 17% /usr
/dev/md2 7.9G 7.9G 0 100% /var

/var/spool/sysklog.d/dev
7.9G 7.9G 0 100% /var/lib/named/chroot/dev
/var/named 7.9G 7.9G 0 100% /var/lib/named/chroot/var/named

When I go to these dirs using a scp client the files show 0 bytes.
Same if I ls -s the dir contents.
What is using all the space?

Fixed.
lsof | grep deleted command showed me that a bunch of files had been deleted and restarting the both httpd and proftpd released the "ghost" files.

Hope this helps someone.