Delete old backup prior to new backup

Hi

I have proxmox doing snapshot backups to a series of 1Tb hotswap USB disks which get rotated each night. This has been working fine until the backup job grew over 500Gb. As VZdump deletes the old backup after a successful backup we are running out of space each night and have to manually go in and delete the old backup each day to get a successful backup.

We currently have Max Backups set to 1 on the USB storage. If we set that to 0 does that disable the Max Backups threshold and not remove any? or would that delete the old backup file first?

I have come across the VZdump hool script option so I guess I could create a script that runs at job-start to remove the old backup prior to running the backup.

I just wondered if there is another way to automate this and will this break if somebody tweaks the backup job in the gui?

Many thanks