You can use the netdiag -t command to diagnose problems with the transport layer in your storage system.
A storage system whose TCP window size is smaller than the recommended value displays the following output:
Performing transport layer diagnostics..... The TCP receive window advertised by CIFS client 192.0.2.13 is 8760. This is less than the recommended value of 32768 bytes. You should increase the TCP receive buffer size for CIFS on the client. Press enter to continue.