/var/lib/docker/overlay2 increases after executing a ReaR backup

Issue

• /var/lib/docker/overlay2 increases after executing a ReaR backup:

# Wrote ISO image: /var/lib/rear/output/rear-controller-0.iso (512M)
[root@controller-0 heat-admin]# df -h | grep overlay
overlay          40G   32G  8,1G  80% /var/lib/docker/overlay2/44ad03c4ac713c7821b6b5cbd33fdc322f475a1800be6b62da9c76f9c5f31484/merged
overlay          40G   32G  8,1G  80% /var/lib/docker/overlay2/02cadca17dbed7f0b8941baaaa364508e840894aa7e51a6727604fe2884e05a5/merged
overlay          40G   32G  8,1G  80% /var/lib/docker/overlay2/8cad0a4c7c4350d949ead3b51e87832d09593491d02c97898132424fbdc7d4b9/merged
overlay          40G   32G  8,1G  80% /var/lib/docker/overlay2/3e27f4ff03cfc9e1c80a7bc8d9a52ede0491d2ef9ddbef0fd23670cb56e96d59/merged

# Wrote ISO image: /var/lib/rear/output/rear-controller-0.iso (512M)
[root@controller-0 heat-admin]# df -h | grep overlay
overlay          40G   34G  6,9G  83% /var/lib/docker/overlay2/44ad03c4ac713c7821b6b5cbd33fdc322f475a1800be6b62da9c76f9c5f31484/merged
overlay          40G   34G  6,9G  83% /var/lib/docker/overlay2/02cadca17dbed7f0b8941baaaa364508e840894aa7e51a6727604fe2884e05a5/merged
overlay          40G   34G  6,9G  83% /var/lib/docker/overlay2/8cad0a4c7c4350d949ead3b51e87832d09593491d02c97898132424fbdc7d4b9/merged

# Wrote ISO image: /var/lib/rear/output/rear-controller-0.iso (512M)
root@controller-0 ctl_plane_backups]# df -h | grep overlay
overlay          40G   35G  5,9G  86% /var/lib/docker/overlay2/44ad03c4ac713c7821b6b5cbd33fdc322f475a1800be6b62da9c76f9c5f31484/merged
overlay          40G   35G  5,9G  86% /var/lib/docker/overlay2/02cadca17dbed7f0b8941baaaa364508e840894aa7e51a6727604fe2884e05a5/merged
overlay          40G   35G  5,9G  86% /var/lib/docker/overlay2/8cad0a4c7c4350d949ead3b51e87832d09593491d02c97898132424fbdc7d4b9/merged

# Wrote ISO image: /var/lib/rear/output/rear-controller-0.iso (512M)
[root@controller-0 ctl_plane_backups]# df -h | grep overlay
overlay          40G   36G  5,0G  88% /var/lib/docker/overlay2/44ad03c4ac713c7821b6b5cbd33fdc322f475a1800be6b62da9c76f9c5f31484/merged
overlay          40G   36G  5,0G  88% /var/lib/docker/overlay2/02cadca17dbed7f0b8941baaaa364508e840894aa7e51a6727604fe2884e05a5/merged
overlay          40G   36G  5,0G  88% /var/lib/docker/overlay2/8cad0a4c7c4350d949ead3b51e87832d09593491d02c97898132424fbdc7d4b9/merged

# Wrote ISO image: /var/lib/rear/output/rear-controller-0.iso (512M)
[root@controller-0 ctl_plane_backups]# df -h | grep overlay
overlay          40G   37G  3,3G  92% /var/lib/docker/overlay2/44ad03c4ac713c7821b6b5cbd33fdc322f475a1800be6b62da9c76f9c5f31484/merged
overlay          40G   37G  3,3G  92% /var/lib/docker/overlay2/02cadca17dbed7f0b8941baaaa364508e840894aa7e51a6727604fe2884e05a5/merged
overlay          40G   37G  3,3G  92% /var/lib/docker/overlay2/8cad0a4c7c4350d949ead3b51e87832d09593491d02c97898132424fbdc7d4b9/merged

# Wrote ISO image: /var/lib/rear/output/rear-controller-0.iso (512M)
[root@controller-0 ctl_plane_backups]# df -h | grep overlay
overlay          40G   39G  2,0G  96% /var/lib/docker/overlay2/44ad03c4ac713c7821b6b5cbd33fdc322f475a1800be6b62da9c76f9c5f31484/merged
overlay          40G   39G  2,0G  96% /var/lib/docker/overlay2/02cadca17dbed7f0b8941baaaa364508e840894aa7e51a6727604fe2884e05a5/merged
overlay          40G   39G  2,0G  96% /var/lib/docker/overlay2/8cad0a4c7c4350d949ead3b51e87832d09593491d02c97898132424fbdc7d4b9/merged