part_max_used value different with df -h show

[legendtkl]

Hello, my os info is as follow.

[root@emr-header-1 proc]# lsb_release -a
LSB Version:	:base-4.0-amd64:base-4.0-noarch:core-4.0-amd64:core-4.0-noarch
Distributor ID:	CentOS
Description:	CentOS release 6.5 (Final)
Release:	6.5
Codename:	Final

When I type df -h, it shows.

# df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/vda1        40G   15G   24G  39% /
tmpfs           7.8G  520M  7.3G   7% /dev/shm
/dev/vdb         79G  3.2G   72G   5% /mnt/disk1

But Ganglia's RRD file shows

# rrdtool fetch -r 300 part_max_used.rrd AVERAGE
1500275100: 4.1300000000e+01
1500275400: 4.1300000000e+01
1500275700: 4.1300000000e+01
1500276000: 4.1300000000e+01
1500276300: 4.1300000000e+01
1500276600: 4.1300000000e+01
1500276900: 4.1300000000e+01

Is it alright ？