KVM Centos Hdd almost empty, but backup 35G

Good Day,

I m seeing a wierd pattern when i take a backup of one of my KVMs.

I used to have over 40G of data in that kvm centos, then removed all those files/folders not there is only 1G of data in that server. I took a backup of that kvm on proxmox and it took forever and i see that the backup file is over 35G?

What might be the problem here

here is df -h on that kvm centos;
[administrator@svn ~]$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg_svn-lv_root
47G 880M 44G 2% /
tmpfs 120M 0 120M 0% /dev/shm
/dev/vda1 485M 32M 429M 7% /boot