You cannot backup a VDP appliance itself as the data drives are independent persistent and you cannot snapshot them.
If your DR has a VC with ESXi (of essentia+ or higher) Then you can deploy another VDP here and use this as a replication target.
You will be replicating your backup data from VDP1 to VDP2
If you do not have a vCenter, then a more crude workaround is to manually copy the data disks to a disk to an offline tape.
More about this below:
vSphere Data Protection Backup to Tape - VMware vSphere Blog
Suhas
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Don't Backup. Go Forward!
Rubrik