Attach it to the VM

Is this possible only with the extra, bought storage boxes ? Or is this possible even with the free 100G backup boxes offered with each dedicated machine ? (Or is this just nfs mount?)

We have a dedicated machine in a project from Hetzner with big raided hard disks but the latency is starting creep up on us, moving some of the data off to the faster ssd/san boxes would be rather helpful.