You could try to dump the EEPROM and get a hold of the user password or override it by reprogramming it.

I guess the network will be a bottleneck on Garage too. If you want high performance you might need a hybrid solution, like clustering of stateful apps on local storage as well as periodic full backups on a distributed storage.

Longhorn is pretty easy to use. Garage works well too. Ceph is harder to use but provides both block and object storage (s3).