Ethernet monitoring unit network configuration

The Ethernet monitoring unit (EMU) is a separate server connected to the network switches using mirror ports or Switch Port Analyzer 'SPAN' ports. These ports are configured to mirror packets flowing to the ports connected to the storage links. The EMU is designed to parse every packet it receives to determine information about operations and endpoint IP addresses. This information includes:

The OnCommand Insight server and the EMU server do not require access to the production VLAN traffic. The OnCommand Insight server needs connectivity to the storage array via the management VLAN. The EMU needs connectivity to the Insight server, potentially over the management VLAN. The connectivity between the EMU and the switch connected to the storage array is by way of the mirror ports only. For this configuration, no VLAN connectivity or IP addresses are required for the EMU.

The switches can be 1GbE or 10GbE capable. The amount of traffic on the switch can exceed the capability of the mirror port. Enterprise grade switches expect this to happen and will drop packets in a first-come, first-served basis, without causing network utilization issues. The recommendation is that the mirror port is 10GbE, however 1GbE ports will work, but with a higher probability of packets being dropped. When packets are dropped, the EMU receives a representative portion of all the traffic. Under these overloaded network circumstances, the server creating the load and the degraded resources continue to be visible in the correct proportions but with lower fidelity.

The illustration below is a simple representation of an Ethernet topology containing an EMU. Clients (any number of physical Hosts or Virtual Machines) are accessing NAS shares accessible through a set of Ethernet switches to a number of storage systems. Ethernet NAS traffic is flowing between the storage systems and the clients.

Supported platforms

The following hardware platforms are supported for this release of Ethernet monitoring:
  • ONTAP 9.0
  • Clustered Data ONTAP
  • Data ONTAP 7-Mode


The following restrictions apply to this release of the EMU:
  • Only Ethernet/-IPv4/NFSv3 traffic is monitored.

    Packets with other protocols are not inspected.

  • If the traffic to the storage array is encrypted, the EMU does not parse the packets.
  • The storage arrays must be monitored by the same OnCommand Insight server that the EMU is connected to.
  • If client servers are not discovered by the OnCommand Insight server, only the IP address of the initiator is displayed.

Ethernet Monitoring Unit monitoring and management

Ethernet Monitoring Units (EMUs) are similar to Acquisition Units (AU). The OnCommand Insight web UI includes an Ethernet Monitoring Units administration screen which allows you to perform the following operations:

  • View status messages for the EMU
  • Restart the EMU
  • Delete an EMU (provided it is not in "Active" status)
  • Access the EMU landing page

The EMU landing page is similar to a Data source status page. It presents the overall status of the single EMU Data source. The EMU detail shows the polling status for the last 3 weeks, provides the ability to generate an error report, and the ability to install a Patch.