Configuring the tiebreaker
Configure a tiebreaker for cluster environments with an even number of nodes.
System Automation for Multiplatforms requires the majority of nodes to be online in the domain to start automation actions. If the domain consists of an even number of nodes, it might happen that exactly half of the nodes of the domain are Online. In this case, System Automation uses a tiebreaker to decide the quorum state, which determines whether automation actions can be started (HAS_QUORUM), or if no automation actions are possible (PENDING_QUORUM, NO_QUORUM).
Configure a shared disk tiebreaker such as ECKD or SCSI by using the IBM.TieBreaker resource class. Additionally two tie breakers are predefined, operator and fail. The operator tiebreaker provides an undetermined result when a tie occurs and it is left to the administrator to resolve the tie through granting or denying the operational quorum. When a tie occurs and a tiebreaker of type Fail is active, the attempt to reserve the tiebreaker is always denied. The default tie breaker type is set to Operator.
Additional implementations of a tiebreaker can be added by using the tiebreaker type EXEC. System Automation for Multiplatforms provides a network and an NFS tiebreaker as additional tiebreaker implementations.
lsrsrc -c IBM.TieBreaker
Resource Class Persistent Attributes for: IBM.TieBreaker
resource 1:
AvailableTypes ={["SCSI",""],["EXEC",""],["Operator",""],["Fail",""]}
lsrsrc IBM.TieBreaker
Output:
Resource Persistent Attributes for: IBM.TieBreaker
resource 1:
Name = "FAIL"
Type = "FAIL"
DeviceInfo = ""
ReprobeData = ""
ReleaseRetryPeriod = 0
HeartbeatPeriod = 0
PreReserveWaitTime = 0
PostReserveWaitTime = 0
NodeInfo = {}
resource 2:
Name = "Operator"
Type = "Operator"
DeviceInfo = ""
ReprobeData = ""
ReleaseRetryPeriod = 0
HeartbeatPeriod = 0
PreReserveWaitTime = 0
PostReserveWaitTime = 0
NodeInfo = {}
resource 3:
Name = "myTieBreaker"
Type = "SCSI"
DeviceInfo = "ID=0 LUN=0 CHAN=0 HOST=2"
ReprobeData = ""
ReleaseRetryPeriod = 0
HeartbeatPeriod = 5
PreReserveWaitTime = 0
PostReserveWaitTime = 0
NodeInfo = {}
resource 4:
Name = "mytb"
Type = "EXEC"
DeviceInfo = "PATHNAME=/usr/sbin/rsct/bin/samtb_net
Address=192.168.177.2"
ReprobeData = ""
ReleaseRetryPeriod = 0
HeartbeatPeriod = 30
PreReserveWaitTime = 0
PostReserveWaitTime = 30
NodeInfo = {}
ActivePeerDomain = "21"
IBM.TieBreaker
, only one of them can be active in the cluster at
the same time. Enter the following command to list the tiebreaker that is active in the
cluster: lsrsrc -c IBM.PeerNode OpQuorumTieBreaker
Output:
Resource Class Persistent Attributes for: IBM.PeerNode
resource 1:
OpQuorumTieBreaker = "Operator"
chrsrc -c IBM.PeerNode OpQuorumTieBreaker="Operator"
Enter the
following command to grant or deny the operational quorum when tiebreaker is Operator:
runact -c IBM.PeerDomain ResolveOpQuorumTie Ownership=1 (0 to deny)