Crossover cables as heartbeat LAN?

[Duncan Edmonstone]

A colleague was telling me the other day that serviceguard now supports the use of crossover cables for heartbeat LANs in 2 node clusters - Is this the case? It certainly wasn't 18 months ago when I last spoke to HP about this. Can someone point me to any documentation that states this?

[Animesh Chakraborty]

Hi,
You can use serial cable in case of two node cluster.
May be your colleague was refering that.



Thanks
Animesh

[Robin Wakefield]

Hi Duncan,

Check the following previous thread:

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x04a6854994d9d4118fef0090279cd0f9,00.html

We have been using crossover for heartbeat for over 3 years, supported by HP. The thread highlights the potential problems.

Rgds, Robin.

[Rainer von Bongartz]

Duncan,

I use a cross over cable since two years for MC/SG heartbeat and I'm not aware that this isn't supported.

[melvyn burnard · Accepted solution]

Using a crossover cable for a heartbeat lan is and has been supported for some time now, but I generally recommend not using it for various reasons. I can, however, quote the official support statement:

We often get questions asking whether Crossover cables are supported for use in a ServiceGuard cluster. The short answer is YES, but there are some important issues that you should be aware of:

This solution only works in a two node cluster. There is no way to have a Standby LAN card when using a Crossover LAN cable.

When either LAN card fails, or the crossover cable is disconnected, both LAN cards go down. This is because the electrical signals necessary for the cards to determine that a valid LAN connection exists are not present. The result is that since both nodes appear to have a bad LAN card, ServiceGuard may TOC the wrong node. If a hub was used between the two LAN cards, then the hub would provide the electrical signals to the other card, allowing it to stay up.

On multi-speed cards, such as 10/100Base-T, the cards must negotiate which speed will be used when the system boots up. If only one system is booted and the remote system is down, then the negotiation will fail, and the card will not be enabled at all. So when the second node eventually comes up, it's LAN will also be down. If a hub is used, then the negotiation will succeed, so the LAN cards will come up at bootup, even if only one node is running.
It may be possible to force some multi-speed LAN cards to bypass the negotiation at bootup and to use a predetermined fixed speed. If this is possible, then would allow the two systems to boot up at different times and still use the Crossover cable connected LAN cards once they are both booted up.

Since both cards may go down when there is a failure when a Crossover cable is used, it can be difficult to determine where the problem lies. Another problem using Crossover cables is that if they are not properly labeled, they may accidently be used in situations where they will not work.

For the reasons listed above, HP does not recommend using Crossover cables for ServiceGuard configurations. However, they are
still supported as long as you are willing to accept the above limitations. Using a Crossover cables is cheaper than using a hub, but it compromises the HA solution.

Hope that clears it up.

[Duncan Edmonstone]

Thanks for all your replies guys. Looks like in my previous experience of this I was confusing 'not supported' with 'not advised'. I will assign points as soon as my hideously slow web connection allows...

[Alexander M. Ermes]

Hi there.
Yes it is possible. We run a cluster of two N4000 machines since last year December and it works perfekt. A hub or a switch would give you an additional point of failure.
Rgds
Alexander M. Ermes