Azure Backup uses incremental snapshots of managed disks that store only the delta changes to disks since the last snapshot on Standard HDD storage, regardless of the storage type of the parent disk. For more reliability, incremental snapshots are stored on Zone Redundant Storage (ZRS) by default in regions that support ZRS. Currently, Azure Disk Backup supports operational backups of managed disks that don't copy the backups to Backup vault storage. So the backup storage redundancy setting of the Backup vault doesn't apply to the recovery points.