[ClusterLabs] question about equal resource distribution

[Kristoffer Grönlund]

Ilia Sokolinski <ilia at clearskydata.com> writes:

> Suppose I have a N node cluster where N > 2 running m*N resources. Resources don’t have preferred nodes, but since resources take RAM and CPU it is important to distribute them equally among the nodes.
> Will pacemaker do the equal distribution, e.g. m resources per node?
> If a node fails, will pacemaker redistribute the resources equally too, e.g. m * N/(N-1) per node?
>
> I don’t see any settings controlling this behavior in the documentation, but perhaps, pacemaker tries to be “fair” by default.
>

Yes, pacemaker tries to allocate resources evenly by default, and will
move resources when nodes fail in order to maintain that.

There are several different mechanisms that influence this behaviour:

* Any placement constraints in general influence where resources are
  allocated.

* You can set resource-stickiness to a non-zero value which determines
  to which degree Pacemaker prefers to leave resources running where
  they are. The score is in relation to other placement scores, like
  constraint scores etc. This can be set for individual resources or
  globally. [1]

* If you have an asymmetrical cluster, resources have to be manually
  allocated to nodes via constraints, see [2]

[1]: http://clusterlabs.org/doc/en-US/Pacemaker/1.1-pcs/html-single/Pacemaker_Explained/index.html#s-resource-options
[2]: http://clusterlabs.org/doc/en-US/Pacemaker/1.1-pcs/html-single/Pacemaker_Explained/index.html#_asymmetrical_opt_in_clusters

Cheers,
Kristoffer

> Thanks 
>
> Ilia Sokolinski
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-- 
// Kristoffer Grönlund
// kgronlund at suse.com