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 failure is the same as the

Package P1 continues to run

In this scenario, no attempts are

previous failure except that the

on N1 after the first failure

made to repair the first failure

package (P1) is configured with

with md0 consisting of only

until the second failure occurs.

RPO_TARGET set to 60 seconds.

S1

Typically, the second failure occurs

In this case, initially the

After the second failure,

before the first failure is repaired.

 

package (P1) is running on N 1.

package P1 fails over to N2

1. To recover from the first

P1 uses a mirror md0 consisting

and starts with S2. This

failure, restore the FC links

of S1 (local to node N1 -

happens because the disk

between the data centers. As a

/dev/hpdev/mylink-sde) and

S2 is non-current by less

result, S1

S2 (local to node N2). The first

than 60 seconds. This time

(/dev/hpdev/mylink-sde) is

failure occurs when all FC links

limit is set by the

accessible from N2.

between the two data centers

RPO_TARGET parameter.

2. Run the following command to

fail, causing N1 to lose access to

Disk S2 has data that is

S2 and N2 to lose access to S1.

older than the other mirror

add S1 to md0 on N2:

After the package resumes

half S1.

# mdadm --add /dev/md0

 

activity and runs for 20 seconds,

However, all data that was

/dev/hpdev/mylink-sde.

a second failure occurs causing

written to S1 after the FC

This command initiates the

N 1 to fail, perhaps due to power

link failure is lost

re-mirroring process. When it is

failure.

 

 

 

 

complete, the extended distance

 

 

 

 

 

 

cluster detects S1 and accepts it as

 

 

 

md0 again.

 

 

 

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

 

 

 

 

Chapter 4

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