HP Serviceguard Extended Distance Cluster for Linux A.12.00.00 Deployment Guide, March 2014

6 Disaster Scenarios and Their Handling
The previous chapters provided information on deploying Software RAID in your environment. In
this chapter, you will find information on how Software RAID addresses various disaster scenarios.
All the disaster scenarios described in this section have the following three categories:
• Disaster Scenario
Describes the type of disaster and provides details regarding the cause and the sequence of
failures leading to the disasters in the case of multiple failures.
• What happens when this disaster occurs
Describes how the Extended Distance Cluster software handles this disaster.
• Recovery Process
After the disaster strikes and necessary actions are taken by the software to handle it, you
need to ensure that your environment recovers from the disaster. This section describes all the
steps that an administrator needs to take to repair the failures and restore the cluster to its
original state. Also, all the commands listed in this column must be executed on a single line.
The following table lists all the disaster scenarios that are handled by the Extended Distance Cluster
software. All the scenarios assume that the setup is the same as the one described in “Extended
Distance Clusters” (page 11) of this document.
Table 4 Disaster Scenarios and Their Handling
Recovery ProcessWhat Happens When This Disaster
Occurs
Disaster Scenario
Multiple Device (MD) driver
As the network and both the mirrored disk sets are
accessible on Node 2, and were also accessible
when Node 1 failed, you only need to restore Node
1. Then you must enable the package to run on
Node 1 after it is repaired by running the following
command:
# cmmodpkg -e P1 -n N1
The package (P1) fails over to
another node (Node 2).
This node (Node 2) is configured to
take over the package when it fails
on Node 1.
A package (P1) is running
on a node (Node 1). Node
1 experiences a failure.
Once you restore power to S1, or restore the FC
links to S1, the corresponding mirror half of S1 (
/dev/hpdev/mylink-sde ) is accessible from
Node 1.
NOTE: Manual intervention is required to add
back a disk to MD device on SUSE Linux Enterprise
Server. For more information, see Troubleshooting
serviceguard-xdc packages.
The package (P1) continues to run
on Node 1 with the mirror that
consists of only S2.
A package (P1) is running
on a node (Node 1). The
package uses a mirror (md0)
that consists of two storage
components - S1 (local to
Node 1 -
/dev/hpdev/mylink-sde)
and S2 (local to Node 2).
Access to S1 is lost from
both nodes, either due to
power failure to S1 or loss
of FC links to S1.
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