Cisco MDS Smart Zoning

I was doing some reading this morning on the new MDS 9710 Director Class switch and came across a feature I hadn’t heard of before. The feature is called “Smart Zoning” and is a real godsend for SAN and data center administrators.

Traditionally SAN admins that follow best practices follow the “single initiator”, “single target” rule for zoning FC fabrics. There are a couple reasons why this is a best practice:

1. Keep SAN traffic generated by devices in other zones isolated. Traffic like Registered State Change Notifications (RSCN)
2. FC switch hardware resources. For every 2 members in a zone that communicate with each other two ACEs (Access Control Entries) are created in the TCAM (Ternary Content Addressable Memory). One entry that permits the host to receive traffic from another host/target and another ACE for the opposite direction. The more members in a zone the more pairs of ACEs that are consumed in the TCAM.

Smart Zoning allows the SAN admin to define which members are targets and which members are initiators. Since targets (SAN front-end ports) do not usually need to talk to targets and initiators (host HBAs) do not need to talk to initiators there isn’t a need for ACEs to get created for target-to-target and initiator-to-initiator.

With Smart Zoning a host will only need a single zone in each fabric instead of the typical 2-4 zones per fabric. The number of zones a host needs depends on how many SAN front-end ports the host needs access to.

Take for example 10 Cisco UCS ESXi hosts that need to access LUNs on an EMC VNX 5500.

• Each host will have 2 vHBAs; one in each SAN fabric
• EMC VNX will have 4 SP front-end ports in each fabric
• Each host vHBA will need to communicate with 4 EMC VNX ports in each fabric

Typically this configuration would look something like this for a single host. Multiple this out for 10 hosts and you have 40 zones needed in each FC fabric.

zone name vnx_spa0-esx01_vmhba1 vsan 200
member device-alias vnx_spa0
member device-alias esx01_vmhba1

zone name vnx_spa2-esx01_vmhba1 vsan 200
member device-alias vnx_spa2
member device-alias esx01_vmhba1

zone name vnx_spb1-esx01_vmhba1 vsan 200
member device-alias vnx_spb1
member device-alias esx01_vmhba1

zone name vnx_spb3-esx01_vmhba1 vsan 200
member device-alias vnx_spb3
member device-alias esx01_vmhba1

With Smart Zoning the configuration would look like this. Note the keyword target or init after the device-alias name. The number of ACEs consumed in the TCAM is the same but the administrative effort is dramatically reduced. The number of zones needed in each fabric goes from 40 to just 10.

zone name vnx_spa_b-esx01_vmhba1 vsan 200
member device-alias vnx_spa0 target
member device-alias vnx_spa2 target
member device-alias vnx_spb1 target
member device-alias vnx_spb3 target
member device-alias esx01_vmhba1 init

There are some requirements for Smart Zoning that should be verified before trying to use this feature:

• NX-OS 5.2(6) or greater is required
• Only supported on MDS 9000/9500s or Nexus 7000 with NX-OS 6.1 or greater
• Smart Zoning is not configurable on Nexus 5000/5500 series switches. I really don’t know why Cisco does things like this, I really wish they would make NX-OS for all devices parity with each other.
• For multi-switch fabrics every switch in the fabric must have NX-OS 5.2(6) or greater and support Smart Zoning. This rules out Nexus 5500s unless they are in NPV mode.
• Here is a screen shot I got from someone at Cisco

To enable the feature:

switch# conf t
switch(config)# zone smart-zoning enable vsan 200

or to enable it as the default zoning mode for all VSANs on the switch

switch# conf t
switch(config)# system default zone smart-zone enable

Next for each zone define which members are targets and which members are initiators (see above zone example)

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