Post-upgrade task for cluster using IBM Storage Scale replication

During or after the pureScale instance upgrade from a version prior to 12.1, you are required to manually convert the tiebreaker redundancy group ID from 3 to 4. This task is an online operation.

Before you begin

Important: To run the db2cm utility as the root user, ensure the DB2INSTANCE environment variable is set to the instance owner.

Ensure that you have root access before you begin this task.

About this task

In a cluster with IBM® Storage Scale replication, the redundancy group IDs 1 and 2 are assigned to represent the two data replicas, and ID 4 is assigned to the tiebreaker. ID 3 is reserved for the third data replica in IBM Storage Scale.

The following procedure describes the steps to convert a tiebreaker redundancy group ID from 3 to 4 in a IBM Storage Scale replication.

Procedure

Verify if any tiebreaker disk in the file system is associated with 3 as its redundancy group ID using the following command run under root:

/usr/lpp/mmfs/bin/mmlsdisk <fs-name>

Note: The parameter must be prefixed by a /dev/xxx, the user can issue the command "/usr/lpp/mmfs/bin/mmlsfs all -A" to find <fs-name>

For example: /usr/lpp/mmfs/mmlsdisk /dev/db2fs1

If the redundancy group ID 3 is used for the tiebreaker, run the following command to convert it from 3 to 4:

Create a stanza file with content:
```
%nsd:
  nsd=<NsdName>
  failureGroup=4
```

Apply the redundancy group ID change using the stanza file:

/usr/lpp/mmfs/bin/mmchdisk <fs-name> change -F <stanza file>

Rebalance the file system using db2cm utility:
```
db2cm -cfs -rebalance -filesystem <fs-name>
```
Note: Rebalancing of data can be I/O intensive and the duration depends on the size of data. It is recommended to run them at off-peak usage hours. The prefix `/dev/` must be removed from the parameter.
For example: ./db2cm -cfs -rebalance -filesystem db2fs1