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The case for a separate VLAN for Heartbeats

Hi All

Background:

We're building 2 UCS domains with Windows Server 2012 (on physical blades) servers across 2 geographical sites. These servers will be grouped in AlwaysOn Availability groups (SQL Server 2012) with 4 nodes (2 from each site) per availability group. A key requirement for an availability group is that all nodes in it must be able to exchange heartbeat messages via unicast and UDP at port 3343. Microsoft supports routed VLANs for multi-site (multi-subnet) heartbeat for Windows/SQL 2012. The storage is accessed via FCoE.

Question:

(1) Given the converged infrastructure with UCS, heartbeat messages will share the same network path as the public interface. So, is there a need for a separate VLAN for heartbeats? Or can the public interface be used? Microsoft supports both separate VLAN and using the public interface. However, I'm trying to see the benefit with a separate VLAN given the converged infrastructure.

(2) We can QoS Heartbeat and Public VLANs giving Heartbeat a higher  priority (as Heartbeats are latency sensitive), but with such high network bandwidth within the UCS domain, is it really worth doing this (setting up QoS on FI and  Nexus 5K)?

Comments:

(1) Separate Heartbeat network makes most sense if it is on a completely different network path as that of the public network. The crossover cable is a good option for servers in adjacent racks (no dependency on switches).

(2) Even if you place heartbeat and public VLANs on different Fabrics, failover will bring them together.

(2) As I see it, the only guaranteed separation between Heartbeat and public within UCS is on te Blade where we could use separate adapters (we use B200 M3), but this makes the costs prohibitive and not much sense if the paths are shared beyond the adapter.

Your feedback is most welcome.

Thank You

JJ

1 REPLY
New Member

The case for a separate VLAN for Heartbeats

Well, http://social.technet.microsoft.com/Forums/windowsserver/en-US/fa702a73-0895-436c-b554-dfb3c92d8a0a/failover-cluster-heartbeat-on-a-separate-vlan addresses my question. As Neil Frick states, using a separate physical LAN makes sense for Heartbeats due to the removal of an SPOF. My Network admins and I had a similar discussion on administrative overhead Vs risks (e.g. congestion) and henced discussed QoS....but we find the administrative overhead to far outweigh the risks and will probably go with combining heartbeats with data/public VLAN.

Still, it's good to know what you folks are doing out there as more use-cases will help the community. Thank you.

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