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

Table 4 Disaster Scenarios and Their Handling (continued)
Recovery ProcessWhat Happens When This Disaster
Occurs
Disaster Scenario
Complete the following procedure to initiate a
recovery:
1. Restore data center 1, Node 1 and storage 1.
Once Node 1 is restored, it rejoins the cluster.
Once S1 is restored, it becomes accessible from
Node 2.
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.
2. Enable P1 to run on Node 1 by running the
following command:
# cmmodpkg -e P1 -n N1
The package (P1) fails over to Node
2 and starts running with the mirror
of md0 that consists of only the
storage local to node 2 (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)
Data center 1 that consists
of Node 1 and P1
experiences a failure.
NOTE: In this example,
failures in a data center are
instantaneous. For example
- power failure.
For the first failure scenario, complete the following
procedure to initiate a recovery:
1. Restore the links in both directions between the
data centers. As a result, S2
(/dev/hpdev/mylink-sdf ) is accessible
from N1 and S1 is accessible from N2.
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 N1 after the first failure, with
md0 consisting of only S1.
After the second failure, the
package (P1) fails over to N2 and
starts with S1. Since S2 is also
accessible, the extended distance
cluster adds S2 and starts
re-mirroring of S2.
This is a multiple failure
scenario where the failures
occur in a particular
sequence in the
configuration that
corresponds to figure 2
where Ethernet and FC links
do not go over DWDM.
The package (P1) is running
on a node (N1). P1 uses a
mirror md0 consisting of S1
(local to node N1,
say/dev/hpdev/
mylink-sde) and S2 (local
to node N2 ) .
The first failure occurs with
all FC links between the two
data centers failing, causing
N1 to lose access to S2 and
N2 to lose access to S1.
After recovery for the first
failure has been initiated,
the second failure occurs
when re-mirroring is in
progress and N1 goes
down.
40 Disaster Scenarios and Their Handling