Disaster Scenarios and Their Handling

 

 

Table 4-1

Disaster Scenarios and Their Handling (Continued)

 

 

 

 

Disaster Scenario

What Happens When

Recovery Process

This Disaster Occurs

 

 

 

 

 

 

This is a multiple failure

The package (P1) continues

In this scenario, no attempts are

scenario where the failures

to run on Node 1 after the

made to repair the first failure

occur in a particular sequence in

first failure, with the MD0

until the second failure occurs.

the configuration that

that consists of only S1.

Typically the second failure occurs

corresponds to figure 2 where

After the second failure, the

before the first failure is repaired.

Ethernet and FC links do not go

 

package P1 fails over to N2

1. To recover from the first

over DWDM.

 

 

 

and starts with S2. Data

failure, restore the FC links

The RPO_TARGET for the package

that was written to S1 after

between the data centers. As a

P1 is set to IGNORE.

 

the FC link failure is now

 

result, S1 is accessible from

 

 

lost because the

The package is running on Node

N2.

RPO_TARGET was set to

 

1. P1 uses a mirror md0

2. Run the following command to

IGNORE.

consisting of S1 (local to node

 

add S1 to md0 on N2:

N1, - /dev/hpdev/mylink-sde)

 

 

 

and S2 (local to node N2). The

 

# mdadm --add /dev/md0

first failure occurs when all FC

 

/dev/hpdev/mylink-sde

links between the two data

 

This command initiates the

centers fail, causing Node 1 to

 

 

re-mirroring process. When it

lose access to S2 and Node 2 to

 

 

is complete, the extended

lose access to S1.

 

 

 

 

distance cluster detects S1

 

 

 

After sometime a second failure

 

and accepts it as md0.

occurs. Node 1 fails (because of

 

For the second failure, restore N1.

power failure)

 

 

 

 

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

 

 

 

 

90

Chapter 4