Draft Document for Review February 7, 2020 3:15 pm 8464ch06_HW Implement.fm This type of failure is known as Sick But Not Dead (SBND). Even if only a single cluster is in  this condition, the failure can affect the performance or functionality (or both) of other clusters  that are present in the same grid.  Grid-wide consequences for this type of problem can be prevented by a “fence” mechanism  that is available when all machines in the grid are running microcode R4.1.2 or later. The  mechanism isolates the failing box while repair actions are performed. The other clusters in  the grid continue to run without being affected by the unscheduled peer-outage. In this scenario, the failing box cannot recognize that a problem exists and keeps trying to  take part in grid transactions. The other clusters in the grid recognize this condition and run a  “remote fence” action against the sick clus ter. The following new LIBRARY REQUEST  FENCE options are available to customize the fencing process, depending on business  requirements:  GLYPH<SM590000> Remote Cluster Fence Function enablement: GLYPH<SM590000> Primary fence action: – NONE: This setting is the default. Other clusters in the grid cannot perform remote  fencing against the specified cluster (“distri buted-library”) if it fails. Therefore, the  system depends on the ability of the local cluster to detect that something is wrong with  itself.  – ALERT: Other clusters surface an alert only  when they believe that the specified grid  member is having problems. – OFFLINE: Other clusters trigger a force-offline sequence against the specified cluster  to exclude it from grid transactions if the corresponding thresholds are met. If this  primary action fails, a secondary fence action (if enabled) is started. – REBOOT: Other clusters trigger a reboot sequence against the specified cluster if the  corresponding thresholds are met. In some cases, rebooting the SBND cluster is the  best solution and faster recovery. The cluster automatically starts online processing  after the reboot. If the machine fails to be rebooted, a secondary fence action (if  enabled) is started. – REBOFF (reboot and stay offline): Other clusters trigger a reboot sequence against the  specified cluster when the corresponding thresholds are met. This sequence prevents  it from attempting to come online again. Use this option if health checks and  troubleshooting are required the system comes back online again. If the machine fails  to be rebooted, a secondary fence action (if enabled) is started. LI REQ, <composite-library>, FENCE, <ENABLE|DISABLE> The default is  DISABLE . This control allows or disallows the execution of remote cluster  fence actions from the perspective of the entire grid. LI REQ, <distributed-library>, FENCE, ACTION, PRI,  <NONE|ALERT|OFFLINE|REBOOT|REBOFF> This command features the following options: GLYPH<SM590000> Secondary fence action: LI REQ, <distributed-library>, FENCE, ACTION, SEC, <ENABLE|DISABLE> Referred to as “Isolate from grid network”,  this secondary action is triggered against the  specified cluster only if it was previously enabled (default is DISABLE), and the primary  fence action failed. In this case, other clusters automatically run a reconfiguration of the  intercluster network to logically exclude the failing cluster from any grid transactions. This  action is available for offline or reboot primary actions only. Chapter 6. IBM TS7700 implementation  231