Controls the number of TCP connections that the NFS client uses when communicating with each NFS server. The kernel RPC is constructed so that it can multiplex RPCs over a single connection, but multiple connections can be used if desired.
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In general, 1 connection is sufficient to achieve full network bandwidth. However, if TCP cannot utilize the bandwidth offered by the network in a single stream, then multiple connections might increase the throughput between the client and the server.
Increasing the number of connections doesn't come for free though. The price for increasing the number of connections is increased kernel resource usage to keep track of each of the connections.