And another +1 To backup storage. That's actually what ~70-80% of our customers do with their SANs when swtiching to StarWind HCA or even VSAN.
Another interesting approach which I see less often is to use 2 existing SAN boxes as a storage capacity addition to the new HCI, with some of that storage actually mirrored between the SANs through the HCI storage virtualization layer. This is where customers can actually keep both backup and testing workloads without breaking the SANs into islands of resources.