Multi node failover

[unicks]

Ok, I'm going into unchartered Service Guard territory for my level of knowledge, so here it goes.

We want to set up a 6 node cluster (my first cluster over 2 nodes), using a quorum server (my first time). The question is; can more than one node fail over to the standby node? Not at the same time, but say we had one node fail over and the next day a 2nd node crashed, would it be able to fail over to the standby node too, with one node already there? They would be different apps, using different SAN disks.

Thanks in advance,

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[Rita C Workman · Accepted solution]

Nodes can fail over to other nodes provided everything has been configured properly. Remember it is not the 'node' that fails over, but the packages running on the node!!

Also bear in mind when you set up your cluster nodes for failover, the amount of resources the node has will be impacted as more applications are running on it. So in your cluster you might have one or two nodes that are real hardware powerhouses, just for those kind of events.

And when you set your packages for multi-node failover you also want to select what packages will failover and what will NOT failover. So prioritize...what really needs to run.

I love MC/SG

Regards,
Rita

[unicks]

Rita,

Thanks for the quick response and for the confirmation about multi failovers. Is there a way to say allow only two nodes to fail over to the standby. I mean if the packages from two nodes are running on the standby, that no other pacakge from other any node can be started there.

And one other small question, the quorum server, does it need to be in the same subnet as the cluster?

Thanks.

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[Steven E. Protter]

Shalom,

In the package configuration, you can control what nodes it will start on.

If you only want the package to run on two of three nodes, that can be configured.

It is actually pretty well documented, in the package control template.

SEP

[John Bigg]

You can do all sorts of things in the more recent releases. You can control what runs when there are failures by defining package dependencies, package priorities and package weights, for example (excert from the manual):

You define a capacity, or capacities, for a node (in the cluster configuration file), and
corresponding weights for packages (in the package configuration file).

So, you can defined packages to failover from one node to another, but then that package can be failed if another more important package fails over from another node and there are not enough resources. Or you could simply define that one package cannot run on the same node as another and what happens if this is attempted. i.e. which you want to take preference.

I suggest you look at the latest manual to see what you can do. You will probably find the hard part is deciding what you want to happen rather than implementing it.

[unicks]

Thank y'all for the replies, I think I can get this done. I'll take a look at the newer documentation and see what options are available to me.

Beers!

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