VCS - make Service Groups mutually exclusive (can't be on same node in the cluster). But share N+1

[Seyre1972]

Hi,

got a 3 node VCS cluster (RHEL 6, SFHA 6.2.1) N+1 setup

3 x Service Groups, with SG's set to start as below

N1 - SG1

N2 - SG2 + SG3

N3 - hot spare

SG1& SG2 need to be exclusive (not on the same host). Which under normal conditions/if we lose 1 host is catered for. But need to somehow make them exclusive if we lose both N1 and N2 that whichever tries to failover second onto N3 is stopped from starting up.

appreciate any pointers as to how this can be achieved.

regards,

steve

[Walter_Heim]

Hi Steve,

On the cluster nodes you need to set the Limits attribute.  This will place a limit on the server so that it can only run service groups if the node is below the limits.  Here is an example of the command to set this for a server.

   hasys -modify SERVER1 Limits -add  MyLimit 1

Then you need to set your service groups to consume "MyLimit" when it is brought online by setting the Prerequisites attribute.  Here is an example of how to do that.

   hagrp -modify SG1 Prerequisites -add  MyLimit 1

If you don't set Prerequisites for your SG3 group, then the Limits will not apply to it and it can failover between all 3 nodes.

Or you can set the Limit/Prerequisites higher than 1 to impose other logic as needed to control the failover of the service groups.

FYI - we have added advanced settings in the 7.x products to handle this situation better so that you can specify a priority for the service groups so that VCS will take off lower priority service groups to keep higher priority service groups running.  You might want to check out the features in the latest product to see if they better meet your needs in this situation.

Thank you,

Wally