What is the idea behind getting rid of the disk drive?
Disk drives are slow and has unpredictable latency for access. I don't know how they boot the OS on startup but they must have a way to load the kernel into each node.
Disk drives can also be a significant source of failures. By offloading storage to a network storage implementation, disk failures can be encapsulated by the network storage and prevent disk failures from affecting the supercomputer's downtime.