* Clustered NAS systems were developed to make NAS systems more scalable and to give them more performance
 * Uses several filer heads instead of a single one. The filer heads are then connected to storage.
 * __'''Two Arch：'''__
   1. several file heads each have some storage assigned to them.
      * First approach is used by !NetApp (!NetApp-GX)
   2. the filer heads are really gateways from the clients to a parallel file system.             
      * filer heads communicate with the client using NFS over the client network but access the parallel file system on a private storage network.
      * allows the ClusterNAS to be scaled quite large because you can just add more gateways– which also increases aggregate performance because there are more NFS gateways.
      * Used by Isilon. And Panasas, IBM’s GPFS, and other parallel file systems when they are running in a NFS mode.
 * The problem is that you have limited performance to the client because you are using NFS as the communication protocol. Most of the Cluster NAS solutions use a single GigE connection so you are limited to about 90-100 MB/s at most to each client.