Question about instance volumes

[Felipe Arturo Polanco]

Hello,

I am seeing a behavior that I would like to ask about.

I have some instances that instead of having a normal qcow2 disk file, have
a qcow2 file that points to another backing store file.

eg:

<disk type='file' device='disk'>
      <driver name='qemu' type='qcow2' cache='none'/>
      <source file='/mnt/ps4/c6a79f0b-60b2-419c-98af-6ae854f88ad1'/>
      <backingStore type='file' index='1'>
        <format type='raw'/>
        <source file='/mnt/ps4/ddc78c68-47b2-43ef-9109-4c91ebb8bda5'/>
        <backingStore/>
      </backingStore>
      <target dev='vda' bus='virtio'/>
      <serial>c6a79f0b60b2419c98af</serial>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04'
function='0x0'/>
    </disk>

I am reading online that this is seen when there is a snapshot of another
disk file, but I have no snapshots, just a regular Linux server that I
created through the Cloudstack UI.

Any idea of why this would happen? Not all Instances have this backing
storage file.

Thanks,