This example considers a four-node cluster with one network connection per node and one dynamic SmartConnect zone with only four IP addresses.
One IP address will be assigned to each node, as shown in the following figure.
In this scenario, 150 clients are actively connected to each node over NFS using a round-robin connection policy. Most NFSv3 mounted clients perform a nslookup only the first time that they mount, never performing another nslookup to check for an updated IP address. If the IP address changes, the NFSv3 clients have a stale mount and retain that IP address.
Suppose that one of the nodes fails, as shown in the following figure.
A SmartConnect Zone with Dynamic Allocation for IP addresses immediately hot-moves the one IP address on the failed node to one of the other three nodes in the cluster. It sends out a number of gratuitous Address Resolution Protocol (ARP) requests to the connected switch, so that client I/O continues uninterrupted.
Although all four IP addresses are still online, two of them-and 300 clients-are now connected to one node. In practice, SmartConnect can fail only one IP to one other place, and one IP address and 150 clients are already connected to each of the other nodes. The failover process means that a failed node has just doubled the load on one of the three remaining nodes while not disrupting the other two nodes. Therefore, this process results in declining client performance, but not equally. The goal of any scale-out NAS solution must be consistency. To double the I/O on one node and not on another is inconsistent.
