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
In this scenario, no attempts are made to repair the
first failure until the second failure occurs. Typically
the second failure occurs before the first failure is
repaired.
1. To recover from the first failure, restore the FC
links between the data centers. As a result, 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.
For the second failure, restore N1. Once it is
restored, it joins the cluster and can access S1 and
S2.
1. Run the following command to enable P1 to run
on N1
# cmmodpkg -e P1 -n N1
The package (P1) continues to run
on Node 1 after the first failure,
with the MD0 that consists of only
S1.
After the second failure, the
package P1 fails over to N2 and
starts with S2. Data that was written
to S1 after the FC link failure is now
lost because theRPO_TARGET was
set to IGNORE.
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 RPO_TARGET for the
package P1 is set to
IGNORE.
The package is running on
Node 1. P1 uses a mirror
md0 consisting of S1 (local
to node N1, -
/dev/hpdev/mylink-sde)
and S2 (local to node N2).
The first failure occurs when
all FC links between the two
data centers fail, causing
Node 1 to lose access to S2
and Node 2 to lose access
to S1.
After sometime a second
failure occurs. Node 1 fails
(because of power failure)
In this scenario, no attempts are made to repair the
first failure until the second failure occurs. Typically,
the second failure occurs before the first failure is
repaired.
1. To recover from the first failure, restore the FC
links between the data centers. As a result, S1
(/dev/hpdev/mylink-sde) 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.
For the second failure, restore N1. Once it is
restored, it joins the cluster and can access S1 and
S2.
1. Run the following command to enable P1 to run
on N1
# cmmodpkg -e P1 -n N1
Package P1 continues to run on N1
after the first failure with md0
consisting of only S1
After the second failure, package
P1 fails over to N2 and starts with
S2. This happens because the disk
S2 is non-current by less than 60
seconds. This time limit is set by the
RPO_TARGET parameter. Disk S2
has data that is older than the other
mirror half S1. However, all data
that was written to S1 after the FC
link failure is lost
This failure is the same as
the previous failure except
that the package (P1) is
configured with
RPO_TARGET set to 60
seconds.
In this case, initially the
package (P1) is running on
N 1. P1 uses a mirror md0
consisting of S1 (local to
node N1 -
/dev/hpdev/mylink-sde)
and S2 (local to node N2).
The first failure occurs when
all FC links between the two
data centers fail, causing
N1 to lose access to S2 and
N2 to lose access to S1.
After the package resumes
activity and runs for 20
seconds, a second failure
occurs causing N 1 to fail,
perhaps due to power
failure.
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