SOLVED
I've added includeAllDisks 10% in /etc/snmp/snmpd.conf file and restarted snmp
snmpwalk -v 1 -c public localhost .1.3.6.1.4.1.2021.9
UCD-SNMP-MIB::dskIndex.1 = INTEGER: 1
UCD-SNMP-MIB::dskIndex.2 = INTEGER: 2
UCD-SNMP-MIB::dskIndex.3 = INTEGER: 3
UCD-SNMP-MIB::dskIndex.4 = INTEGER: 4
UCD-SNMP-MIB::dskIndex.5 = INTEGER: 5
UCD-SNMP-MIB::dskIndex.6 = INTEGER: 6
UCD-SNMP-MIB::dskIndex.7 = INTEGER: 7
UCD-SNMP-MIB::dskIndex.8 = INTEGER: 8
UCD-SNMP-MIB::dskPath.1 = STRING: /
UCD-SNMP-MIB::dskPath.2 = STRING: /proc
UCD-SNMP-MIB::dskPath.3 = STRING: /sys
UCD-SNMP-MIB::dskPath.4 = STRING: /dev
UCD-SNMP-MIB::dskPath.5 = STRING: /dev/pts
UCD-SNMP-MIB::dskPath.6 = STRING: /proc/bus/usb
UCD-SNMP-MIB::dskPath.7 = STRING: /sys/kernel/security
UCD-SNMP-MIB::dskPath.8 = STRING: /boot
UCD-SNMP-MIB::dskDevice.1 = STRING: /dev/sda3
UCD-SNMP-MIB::dskDevice.2 = STRING: proc
UCD-SNMP-MIB::dskDevice.3 = STRING: sysfs
UCD-SNMP-MIB::dskDevice.4 = STRING: udev
UCD-SNMP-MIB::dskDevice.5 = STRING: devpts
UCD-SNMP-MIB::dskDevice.6 = STRING: usbfs
UCD-SNMP-MIB::dskDevice.7 = STRING: securityfs
UCD-SNMP-MIB::dskDevice.8 = STRING: /dev/sda1
UCD-SNMP-MIB::dskMinimum.1 = INTEGER: -1
UCD-SNMP-MIB::dskMinimum.2 = INTEGER: -1
UCD-SNMP-MIB::dskMinimum.3 = INTEGER: -1
UCD-SNMP-MIB::dskMinimum.4 = INTEGER: -1
UCD-SNMP-MIB::dskMinimum.5 = INTEGER: -1
UCD-SNMP-MIB::dskMinimum.6 = INTEGER: -1
UCD-SNMP-MIB::dskMinimum.7 = INTEGER: -1
UCD-SNMP-MIB::dskMinimum.8 = INTEGER: -1
UCD-SNMP-MIB::dskMinPercent.1 = INTEGER: 10
UCD-SNMP-MIB::dskMinPercent.2 = INTEGER: 10
UCD-SNMP-MIB::dskMinPercent.3 = INTEGER: 10
UCD-SNMP-MIB::dskMinPercent.4 = INTEGER: 10
UCD-SNMP-MIB::dskMinPercent.5 = INTEGER: 10
UCD-SNMP-MIB::dskMinPercent.6 = INTEGER: 10
UCD-SNMP-MIB::dskMinPercent.7 = INTEGER: 10
UCD-SNMP-MIB::dskMinPercent.8 = INTEGER: 10
UCD-SNMP-MIB::dskTotal.1 = INTEGER: 75830464
UCD-SNMP-MIB::dskTotal.2 = INTEGER: 0
UCD-SNMP-MIB::dskTotal.3 = INTEGER: 0
UCD-SNMP-MIB::dskTotal.4 = INTEGER: 10240
UCD-SNMP-MIB::dskTotal.5 = INTEGER: 0
UCD-SNMP-MIB::dskTotal.6 = INTEGER: 0
UCD-SNMP-MIB::dskTotal.7 = INTEGER: 0
UCD-SNMP-MIB::dskTotal.8 = INTEGER: 101086
UCD-SNMP-MIB::dskAvail.1 = INTEGER: 5314680
UCD-SNMP-MIB::dskAvail.2 = INTEGER: 0
UCD-SNMP-MIB::dskAvail.3 = INTEGER: 0
UCD-SNMP-MIB::dskAvail.4 = INTEGER: 10080
UCD-SNMP-MIB::dskAvail.5 = INTEGER: 0
UCD-SNMP-MIB::dskAvail.6 = INTEGER: 0
UCD-SNMP-MIB::dskAvail.7 = INTEGER: 0
UCD-SNMP-MIB::dskAvail.8 = INTEGER: 36384
UCD-SNMP-MIB::dskUsed.1 = INTEGER: 66663800
UCD-SNMP-MIB::dskUsed.2 = INTEGER: 0
UCD-SNMP-MIB::dskUsed.3 = INTEGER: 0
UCD-SNMP-MIB::dskUsed.4 = INTEGER: 160
UCD-SNMP-MIB::dskUsed.5 = INTEGER: 0
UCD-SNMP-MIB::dskUsed.6 = INTEGER: 0
UCD-SNMP-MIB::dskUsed.7 = INTEGER: 0
UCD-SNMP-MIB::dskUsed.8 = INTEGER: 59483
UCD-SNMP-MIB::dskPercent.1 = INTEGER: 93
UCD-SNMP-MIB::dskPercent.2 = INTEGER: 0
UCD-SNMP-MIB::dskPercent.3 = INTEGER: 0
UCD-SNMP-MIB::dskPercent.4 = INTEGER: 2
UCD-SNMP-MIB::dskPercent.5 = INTEGER: 0
UCD-SNMP-MIB::dskPercent.6 = INTEGER: 0
UCD-SNMP-MIB::dskPercent.7 = INTEGER: 0
UCD-SNMP-MIB::dskPercent.8 = INTEGER: 62
UCD-SNMP-MIB::dskPercentNode.1 = INTEGER: 11
UCD-SNMP-MIB::dskPercentNode.2 = INTEGER: 100
UCD-SNMP-MIB::dskPercentNode.3 = INTEGER: 100
UCD-SNMP-MIB::dskPercentNode.4 = INTEGER: 2
UCD-SNMP-MIB::dskPercentNode.5 = INTEGER: 100
UCD-SNMP-MIB::dskPercentNode.6 = INTEGER: 100
UCD-SNMP-MIB::dskPercentNode.7 = INTEGER: 100
UCD-SNMP-MIB::dskPercentNode.8 = INTEGER: 0
UCD-SNMP-MIB::dskErrorFlag.1 = INTEGER: error(1)
UCD-SNMP-MIB::dskErrorFlag.2 = INTEGER: noError(0)
UCD-SNMP-MIB::dskErrorFlag.3 = INTEGER: noError(0)
UCD-SNMP-MIB::dskErrorFlag.4 = INTEGER: noError(0)
UCD-SNMP-MIB::dskErrorFlag.5 = INTEGER: noError(0)
UCD-SNMP-MIB::dskErrorFlag.6 = INTEGER: noError(0)
UCD-SNMP-MIB::dskErrorFlag.7 = INTEGER: noError(0)
UCD-SNMP-MIB::dskErrorFlag.8 = INTEGER: noError(0)
UCD-SNMP-MIB::dskErrorMsg.1 = STRING: /: less than 10% free (= 93%)
UCD-SNMP-MIB::dskErrorMsg.2 = STRING:
UCD-SNMP-MIB::dskErrorMsg.3 = STRING:
UCD-SNMP-MIB::dskErrorMsg.4 = STRING:
UCD-SNMP-MIB::dskErrorMsg.5 = STRING:
UCD-SNMP-MIB::dskErrorMsg.6 = STRING:
UCD-SNMP-MIB::dskErrorMsg.7 = STRING:
UCD-SNMP-MIB::dskErrorMsg.8 = STRING: