If you ever find yourself confronted with a Plesk system that is running out of disk space, and you just want to get rid off all the misconfigured „keep forever“ backups, here’s how to remove them all from the command line:
# remove all stored backups
/usr/local/psa/admin/bin/pmm-ras --get-dump-list | egrep "name=\".*.xml" | awk -F '"' '{ print $2 }' | xargs -I {} /usr/local/psa/admin/bin/pmm-ras --verbose --debug --delete-dump --dump-specification={} --session-path=/var/log/plesk/PMM
# disable all scheduled server / domain backups
plesk db "UPDATE BackupsScheduled SET active = 'false' where obj_type = 'domain'"
plesk db "UPDATE BackupsScheduled SET active = 'false' where obj_type = 'server'"