3 and 4 node heartbeat network

Hi, in our environment we have 2 and 3 node clusters. All of the clusters
are using crossover cables - on the 3 node clusters, each node has a
connection to the other 2 nodes. Our design team is starting the "design"
process for 4 node clusters and recommendations. Where can I find
documentation stating that heart beat crossover cables are only supported on
2 node clusters and that for 3 and greater node clusters you need to use a
hub or switch (2 for redundancy). I think this came about because our
network team didn't like the fact that switch issues caused issues with our
clusters and prefer the crossover cabled.

Also what kind of issues can be expected in a 3 node cluster where each node
is connected to each other node with a crossover cable? (ie A-B B-C C-A)

"omegan99" <> wrote in message
news:581A448C-5E19-4BC3-B733-...
> Hi, in our environment we have 2 and 3 node clusters. All of the clusters
> are using crossover cables - on the 3 node clusters, each node has a
> connection to the other 2 nodes. Our design team is starting the "design"
> process for 4 node clusters and recommendations. Where can I find
> documentation stating that heart beat crossover cables are only supported
> on
> 2 node clusters and that for 3 and greater node clusters you need to use a
> hub or switch (2 for redundancy). I think this came about because our
> network team didn't like the fact that switch issues caused issues with
> our
> clusters and prefer the crossover cabled.

I don't know where it is documented, but common sense says that the nodes
need to be able to communicate with each . Two nodes can use a cross over
cable, but anything beyond that requires a separate non-routable network.
Usually, this is a vlan or a separate dedicated switch.

> Also what kind of issues can be expected in a 3 node cluster where each
> node
> is connected to each other node with a crossover cable? (ie A-B B-C C-A)

I would expect that it just wouldn't work. Of course, it probably would look
like it is working because most people set the public network to be in mixed
mode.


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Interesting, I suspect your team leads were using hubs or low end switches
that didn't support vlans on their network when first starting to use
failover clustering and had a bad experience.

Our thoughts have always been to use a crossover cable when setting up a 2
node failover cluster. Our reasoning is that it meets the physical
requirements and takes away the need for additional hardware and the
resultant complexity and cost. To be blunt, it's cheaper.

On clusters requiring 3 or more nodes we use a managed switch, and setup an
isolated vlan for just the nodes used in that cluster. In a 4 node cluster
we'd use as a minimum of 4 ports on one or more switches. Basically 1 nic
per node, and rely on the public network for redundancy. The vlans ensure
the heartbeat traffic is isolated from the rest of the public network. The
way we look at it is that we already have the switches installed in all of
our server cabinets, with redundant connections back to the core switches,
the unused ports don't really cost us anything extra to use, where as the
installation of additional nics in each node to be able to establish a fully
meshed private network would be expensive. Keep in mind if a node can't talk
directly with the other nodes over the private network it's going to try to
use the public network, so a partial mesh isn't going to work. The more
network cards you add to the server, the more expansion slots you use up,
and eventually you need to go to a larger server just to get the necessary
expansion slots, yeah I know you can buy 4 nic cards, but if your using
direct attached fibre for the shared storage you'll need HBAs, and if your
using iSCSI you'll need even more nics, eventually your out of slots. The
use of vlans and switches reduces the need.

If your still using low end switches and hubs, or you aren't using vlans on
your higher end switches you might want to look into that first. I'm
assuming since your looking at a 4 node cluster that your working for a
larger organization, with the necessary knowledge and expertise to setup the
vlans and manage them. Your cluster team probably needs to talk to your
network team.


"omegan99" <> wrote in message
news:581A448C-5E19-4BC3-B733-...
> Hi, in our environment we have 2 and 3 node clusters. All of the clusters
> are using crossover cables - on the 3 node clusters, each node has a
> connection to the other 2 nodes. Our design team is starting the "design"
> process for 4 node clusters and recommendations. Where can I find
> documentation stating that heart beat crossover cables are only supported
> on
> 2 node clusters and that for 3 and greater node clusters you need to use a
> hub or switch (2 for redundancy). I think this came about because our
> network team didn't like the fact that switch issues caused issues with
> our
> clusters and prefer the crossover cabled.
>
> Also what kind of issues can be expected in a 3 node cluster where each
> node
> is connected to each other node with a crossover cable? (ie A-B B-C C-A)