The architecture of a diskless computer cluster makes it possible to separate servers and storage array.
Any server that acts as a cluster node can be easily exchanged by demand.
The additional abstraction layer between storage system and computing power eases the scale out of the infrastructure.
Most notably the storage capacity, the computing power and the network bandwidth can be scaled independent from one another.
A similar technology can be found in VMScluster (OpenVMS) and TruCluster (Tru64 UNIX).