FCoE Cookbook for HP Virtual Connect Version 4.20 Firmware Enhancements May 2014

49
Benefits
This Multi-Hop FCoE scenario extends convergence beyond the Top of Rack switches but at the same time it preserves
all your Fibre Channel SAN switch investments. Extended convergence offers more flexibility and capital/operational
cost savings.
Nexus 50xx switches have a limited number of 8Gb FC port (5010=6 max, 5020=12 max) so this scenario can help
customers running out of Fibre Channel ports on Nexus 50xx switches by using FCoE links instead of FC to reach the MDS
SAN switches.
Using multiple FCoE uplink ports on each VC module connected to Nexus and on each Nexus connected to the MDS allow
dynamically distribution of the FCoE traffic across the ports using a round robin format.
FCoE Port Channeling increases the high availability and create enough FCoE SAN subscription.
Considerations
Enabling convergence in the extended network requires more careful bandwidth management than a Dual-Hop FCoE
topology. Suitable subscription is crucial to reduce the risk of congestion and slow performance, therefore the use of
Port Channeling is recommended.
The server-to-VC uplink ratio is adjustable. With the current NX software limitations, the server-to-uplink can go up to:
 2:1 with the Nexus 5500 series and VC Flex-10/10D (as few as two servers share one physical Fabric uplink)
 4:1 with the Nexus 5000 series.
The Nexus to the MDS ratio can be as good as 1:1 with up to 4 ports with the Nexus 5000 series and up to 8 ports with
the Nexus 5500 series.
Multiple VSAN support
The number of FCoE networks per Shared Uplink Set is limited to 32. VSAN tagging is not supported for native FC fabrics.
The number of FCoE networks is additionally limited by the 1000 network domain limit.
For this feature to successfully integrate with Cisco Nexus switches, it is important to note that for each FCoE VLAN a
unique FC VSAN must be created and association between the two must be strictly configured as 1-to-1. Mapping of a
single VLAN into multiple VSANs is not supported. This requirement is documented in Cisco’s best practice
recommendations.
All of the FCoE networks will share the same lossless Priority Flow Control (PFC) queue on any specific shared uplink set.
Sharing PFC queue between multiple VSANs will make it possible that traffic from one VSAN may have impact on traffic
from other VSANs. For that reason, it is highly recommended to create enough SAN subscription (i.e. by using a suitable
number of uplink between VC and Nexus but also between Nexus and Cisco MDS) to avoid any over-subscription issues
that would prevent SAN to pause and therefore to impact other VSANs. Therefore the use of an FCoE Port Channel
between the Nexus and MDS switches is highly recommended.