Backup on different levels, one of my clients who I would say has similar ifrastructure uses following approach:
backup on the vm level - backing up snapshot of the entire virtualization guest - at least once a week, always before update/upgrade. These can be big - consider ZFS pool w/ compression and deduplication active - but that is also hw intesive. On the other hand, I don’t think you need to keep more than last two successfull backups.
filesystem level - run rdiff-backup against the / of the filesystem several times a day. SInce it is essentially versioning, you are only backing up new changes. No zetabyte needed here, ext3/4 will do.
drop database somewhere ideally several times a day - even if there are no incidents, your developers will love you.
The recovery strategy is as follows:
pull the guest out of the last vm backup
sync up the files from last rdiff-backup run
discuss w/ the developer DB recovery - or just recover the last backup and hope for the best…