uname -par
AIX oradocs1a 1 7 00F6F8854C00 powerpc

1. df -g
   Filesystem GB blocks Free %Used Iused %Iused Mounted on
   /dev/hd4 0.50 0.23 54% 13938 19% /
   /dev/hd2 3.50 0.38 90% 64075 38% /usr
   /dev/hd9var 5.00 3.36 33% 19845 3% /var
   /dev/hd3 14.00 3.62 75% 8242 1% /tmp
   /dev/hd1 0.25 0.25 2% 70 1% /home
   /dev/hd11admin 0.25 0.25 1% 9 1% /admin
   /proc - - - - - /proc
   /dev/hd10opt 2.50 2.08 17% 9391 2% /opt
   /dev/livedump 0.25 0.25 2% 22 1% /var/adm/ras/livedump
   /dev/ora_lv 49.75 29.73 41% 53879 1% /opt/oracle
   /dev/onlog_lv 9.75 2.15 78% 16 1% /u01/onlinelogs
   /dev/arclog_lv 2047.75 1179.80 43% 536234 1% /u02/archlogs
   /dev/log_lv 49.75 47.67 5% 390705 4% /u03/logs
   /dev/u04data_lv 32768.00 669.78 98% 2268 1% /u04/data
   /dev/u05data_lv 4000.00 1470.37 64% 28 1% /u05/data

Look at this volume:
/dev/u04data_lv 32768.00 669.78 98% 2268 1% /u04/data

Check metrics from agent.

[root@zabbix zabbix]# zabbix_get -s oradocs1a -k vfs.fs.size[/u04/data,pfree]
0.000000

[root@zabbix ]# zabbix_get -s oradocs1a -k vfs.fs.size[/u04/data,free]
719173545984

[root@zabbix]# zabbix_get -s oradocs1a -k vfs.fs.size[/u04/data,total]
0
[root@zabbix]# zabbix_get -s oradocs1a -k vfs.fs.size[/u04/data,used]
16873012498432

Agent binaries for AIX (agent version 2.2.1) downloaded from Zabbix.com.