The problem is that you can end up with larger latency over the network because it still takes a fixed amount of time for nodes to communicate. Even with a 1TB/s link between nodes you can still have a good 30ms between them all adding even more latency. That can be mitigated somewhat by a good protocol that can manage that latency properly (e.g. not blocking while waiting on ACKs and such), it can still end up with far more latency than a few large disks would be (even better now with SSDs). That said I do imagine that some datasets will benefit from this kind of topology (I can imagine that geospatial stuff will do well with that, since you can locate physically close things on a single machine and reduce the amount of talking needed).